So far I really like the new theme system. It will make it alot easier to integrate wordpress into the rest of my site seamlessly. I have been pretty lax about actually making wordpress look like the rest of my site. Real soon now I will accomplish that goal and either change my front page or change wordpress or a mixture of the two.
Version 1.5 has better spam blocking features and now has a blacklist feature. So now I can blacklist domains that have been spamming me recently.
I also finally bothered to change my permalinks structure since the default is really plain. In Options->Permalink you can change the default structure.
I think /archives/%year%/%monthnum%/%day%/%postname%/ is alot better then then ?p=102 I used to have. Makes it alot easier to get to the archives.
No real snafus with the upgrade other then not following the specific 1.2->1.5 instructions.
Looks like the official feeds changed to