Some users have been reporting being dropped into an endless reboot loop after installing the third service pack to Windows XP. Application Development Trends Magazine (fancy name) dug a little deeper into the matter, and came up with some interesting observations. The bug seems to mostly hit AMD desktop machines made by Hewlett-Packard, although some other OEMs have been affected too.
According to a Microsoft MVP, the issue seems to be that HP, and maybe other OEMs too, use the same OEM image on their AMD-based desktops as they do on their Intel-based desktops (laptops appear to be unaffected). The end result is that both images contain the
intelppm.sys power management driver alongside its AMD equivalent,
amdk8.sys. Microsoft points out that such a configuration is unsupported - the knowledge base article was written after the same reboot problem occured after installing SP2. Having both drivers normally doesn't interfere with system operation, however, it does pose problems during the first boot after an SP installation - causing the reboot issue.
The issue, therefore, seems to be originating from lazy OEMs who deliver unsupported configurations to their customers, and not from an inherent problem of SP3. An AMD spokesperson said Microsoft is modifying Windows Update to warn users of AMD machines. The fix for the problem can be found in the MVP's blog post.
Despite these problems, SP3 appears to be delivering a performance boost compared to Windows XP SP2. exo.blog ran the OfficeBench benchmark test on Windows XP SP3, compared it to results from SP2, and concluded that SP3 is 10% faster. SP3 is also twice as fast as Vista SP1, according to these tests.
ExtremeTech compared game test results from SP3 to those of Windows Vista SP1 (and pre-SP1), and concluded that the performance drop in games associated with switching from XP to Vista are now largely gone, making Vista just as fast as XP when it comes to gaming. The methodology appears to be sound; the installations were tested on the same machine, on two identical hard drives that could not interfere with one another during the benchmark because only one was connected to the motherboard during each test.
It seems that as long as your OEM did not ship an unsupported configuration, SP3 is a worthwhile upgrade.