Hannes Magnusson has posted a few useless statistics about the PHP language including:

• Since PHP 3.0.18 (released October 2000) (no, php.net doesn't keep release records before that for some reason) 60 PHP releases have been made.
• There have only been 2 releases in 2009 so far
• The 89th, 121st, 122nd, 194th, 228th, 241st and the 349th day of the year have had 2 releases each
• The 18th week of the year is most likely to have an release, whole 8 releases have been made in that week!
• 26 PHP releases have been on Thursdays

He also includes a snippet of code that can be used to pull together some of these stats yourself (with only a few errors thrown).