Today, I upgraded a loaded server running vBulletin to PHP 5.2.5. That server is running OpenBSD-current, PHP-fastcgi from ports with Suhosin enabled as in default configuration and Lighttpd.
That setup has been very stable for 2 years.
But the upgrade to PHP 5.2.5 was a complete failure. PHP crashed with segmentation faults almost after every request on memory deallocation.
After disabling Xcache, libpuzzle and almost every module, it kept crashing over and over again.
Reverting to 5.2.4 immediately fixed the issue.
I didn’t investigate that bug yet, moreover it doesn’t happen with every script. Anyway, unless you absolutely need the fixes that were applied between PHP 5.2.4 and 5.2.5, maybe it’d better to wait for the next release. Or at least, if you want to upgrade, prepare a rollback procedure first.