I use WordPress for this blog and for several other blogs and podcasts (coupled with PodPress, it is my podcast solution of choice). The platform is great, but I have had quite a time these last few hours of 2008 upgrading to the latest version—WordPress 2.7.
My first challenge involved a 2.0.x version. Needless to say, a lot has changed from that version to 2.7. Most of the issues were centered around UTF-8 database issues. If you really want to know more check out this and that on the WordPress forums.
The second issue seemed to be with the auto-update in Fantastico. I won’t even go into that one. I will, however, say that you should always, always, always back up your files and data before you do any upgrades. I did, and I am breathing a huge sigh of relief because of it. I would also recommend manual updates over any automated methods.