I am trying to go from php4 to php5 and am having a problem. Everything seems to work fine except for themes that have options. You can set the options, but when the page is rendered it ignores the options. Themes without custom options all seem to work fine. I'm guessing I need to change a a file to look for something or change a permission but not sure.
Also, when I changed from php4 to 5 I couldn't log into any blogs that where restricted in any way (to bots or people). I had to revert, unlock the blogs, then change to 5 and restrict.