Felix Geisendorfer has a reminder from developers out there - "PHP 5.2.1 was an evil release":

While I was at php|works I heard a lot of people say how bad of a release 5.2.1 was and that I should stay away from it. Well I didn't take it to seriously at this point, but when I checked what version of PHP we are running on my client project recently it turns out it was 5.2.1.

They were seeing performance issues (database related) so they upgraded to the latest version, 5.2.4, and immediately saw a performance jump of forty to sixty percent and a much lower amount of CPU usage. Upon some further research, he found a certain bug in 5.2.1 that could have been the culprit.