The easiest solution in this case is to rename the "plugins" folder to something else such as "plugins2" and then create a blank "plugins" folder. After this you should be able to login to the WordPress admin screen. You can then copy one plugin at a time from "plugins2" folder to "plugins" verifying that each of them works with the new version. If not, you can download it directly from either the plugin homepage or from WordPress plugin repository.

Another common reason for blank page after WordPress upgrade is the stale cache files. The earlier solution of renaming plugins should work in this case also. You can also delete all the cached files to see whether that works.

Common reasons for blank page in WordPress admin screens are,

1. Incomplete WordPress upgrade - In rare cases, the upgrade process may be interrupted and this can cause blank page problem. The solution in this case is to upgrade again. I usually delete everything under wp-admin and wp-include and then re-upload the same folders from the new version.
2. Extra space at the end of plugin files - If there are any white spaces after the closing tag of PHP code in a plugin, it can cause "Cannot modify header information - headers already sent by" error. Unfortunately sometimes this may not be displayed on screen and you will see only a blank screen.  You need to be careful with white spaces whenever you edit any PHP file in WordPress. The reason for this problem is that the white space after the code is interpreted as HTML code and would be send to the browser as and when encountered.
3. Incompatible plugins - Some of the files you have on your blog may be incompatible with the latest version of WordPress. This could be due to API changes or may be due to low quality plugin code. Either way you need to either upgrade to a new version if there is one or should find an alternative plugin in the WordPress plugin directory.

You can turn on XML-RPC using WordPress dashboard from Settings -> Writing -> XML-RPC option. Refer to the following screen shot,

If you recently upgraded from 2.5.1, you would be wondering what the fuss is all about! Interestingly the above two options are enabled by default when you upgrade from 2.5.1 to 2.6.

You may be wondering why XML-RPC is disabled by default. XML-RPC is used by a lot of hacking tools built around WordPress trying to exploit security vulnerabilities such as weak passwords. So by disabling XML-RPC, a lot of current hacking attempts can be prevented.

But for external tools such as Windows Live Writer, XML-RPC is a must. So in the end it becomes a trade off between flexibility and security. But as long as you keep your WordPress installation updated and use strong passwords, chances of getting hacked is minimal.

Another interesting thing I noticed while configuring Windows Live Writer for a WordPress 2.6 is that WLW is unable to detect WordPress 2.6 installation and RPC configuration. I had to manually select the WordPress and location of the RPC php file as shown below,

This is a good feature if you are using WordPress UI for writing your posts. But if you are using an external tool, you might not need this feature.

One of the problems with post revisions is that if you do a lot of editing, a lot of different versions are generated and are stored in the MySQL db. Over a period of time your database becomes bloated and performance of your blog can get affected. Unfortunately on the WordPress dashboard there is no option to disable post revisions.

So it is no wonder there are couple of plugins being released to add the post revision disabling option. But I am not a fan of plugins because many of the plugins come with security holes and many of them affects performance of the blog. So my mantra is to keep the number of plugins to a bare minimum.

Fortunately there is another way to disable post revisions in WordPress 2.6. You can edit wp-config.php and add the following line it,

This command sets a flag which instructs WordPress to avoid creating versioned copied of a post.  If you replace ‘false’ with a number, WordPress will ensure that the number of version generated for a post is limited by that number.

Another feature recently added to WordPress is the auto save feature. This saves your post every 60 seconds automatically when you are using the WordPress editor. If you don’t want this feature or you want a different interval, you can add the following entry in wp-config.php,

The second parameter indicates the number of seconds after which the post is auto saved. You can set this to a large value to avoid frequent auto saves.

Where does WordPress store post revisions in DB?

You may be wondering where WordPress 2.6 stores post revisions in DB. If you are looking for a new table you are mistaken. All the post revisions are stored in the wp-posts table itself.  For the old revisions the post status is stored as ‘inherit’ and post_type as ‘revision’. The post_parent in this case is set as the id of the currently published post.

How do I delete old revisions of WordPress posts from MySQL DB?

You can use the following SQL script to delete all old revisions from MySQL DB. For large WordPress databases, this will improve performance of the blog.

I detected the problem only when I realized that my blog is no longer in the Google search index!

The WordPress hacking became so widespread that Technorati has special process in place to quarantine infected/hacked WordPress blogs! There are reports of WordPress 2.5 vulnerability, but it is better to upgrade to 2.5 than stick with 2.3.3. The important thing is to upgrade as soon as a release is out rather than cling to a version for which hacking scripts may be sold in warez forums! So I am keeping my thumb on the WordPress upgrade button waiting for 2.5.1 

After the upgrade I came across an interesting  issue when I tried to post through Windows Live Writer. It responded with an error message - Invalid response document returned from XmlRpc server. I initially thought that it is a bug with Windows Live writer and compatibility issue with WordPress 2.5. Then I tried posting the same from the WordPress admin. When I tried to upload an image I got the following error,

- Fatal error: Call to undefined function wp_constrain_dimensions.

Then I realized there is some problem with the WordPress 2.5 upgrade. Here is how I resolved the problem. First I deleted all the php files in the WordPress root folder (except wp-config.php) and then deleted wp-admin and wp-includes folder. After ensuring that all old files are deleted, I uploaded WordPress 2.5 files again. That resolved the issue with Windows Live Writer!

This surprise move by Intel is going to immediately push quad core adoption. Intel’s manufacturing process costs are cheaper than AMD and hence AMD might find it difficult to compete in this area. Also AMD posted a net loss of $358 million for Q1 2008. So this Intel move could be a "terminator" move for AMD! Who knows, Intel might have plans to acquire AMD

Multi core processor power is yet to be completely utilized. We might see a sudden influx of game engines which makes use of multi core architecture.

Here is a summary of the Quad core price cut,

The complete list of Intel price cut is available here (PDF).