I just completed the upgrade of my blog to WordPress 2.6. It took more time that I had anticipated. However, the process was quite educational.
I have upgraded before using the WordPress Auto Updated plugin. After a few clicks, your blog is updated. It is so easy that it is hard to resist. I tried WPAU in order to get to WordPress 2.6, and the process was somewhat interrupted on the final stages. It was not clear what the problem was. The effect however was any access to any page of the blog would result to a blank page. No errors, no warnings whatsoever.
In terms of troubleshooting, it is really annoying not to have some sort of feedback. My visit to #wordpress at Freenode resulted in “oh dude, join the club”. Apparently, the blank page issue is common and it affects many users. I just noticed that Irene’s blog gives a blank page as well; I wonder if she upgraded recently.
There are a few blog posts that debate on the blank page issue; use blogsearch.google.com to find the most fresh of them. The typical blog post on the blank page issue has a standard format with the author dumping a laundry list of things they tried first before mentioning at the end of the post in vague terms what they think the source of the problem is. I will spare of the long list as we are already at the fourth paragraph of the post.
What I believe was the problem is the theme. When you use WPAU, it does not disable the theme since you are upgrading from within the WordPress administration screen. Then, you end up with a new WordPress and a theme that crashes. If you are planning to try WPAU, it might be good to revert to a default theme first.
If you are reading this, then you probably messed up your blog already. You can change the theme using phpmyadmin, by altering the wp_options table. The option_names of interest are template, stylesheet and current_theme. Put default values here.
Overall it was quite educational to go through the details of installing WordPress, picking new theme, dumping old plugins and updating existing ones. What’s needed now is a full backup and hope the blog works until WordPress 3.0.