Personally I don't mind Vista, but there are some occasions where using Windows XP would be better. We know that Windows Vista has higher system requirements than Windows XP, and taking into account the whole Vista Capable fiasco
, there are some users where downgrading to Windows XP would be better.
For example, my HP 2510p notebook originally had Windows Vista Business installed (actually, I replaced the OS with Vista Server 2008 Standard Edition). However, recently I decided to install and use Windows XP instead. It only has a 1.8" 4200RPM hard drive and a Core 2 Duo ULV U7600 processor. I'm glad I changed because my notebook is definitely more responsive now and it takes less time to copy files (most certainly), boot, hibernate and shutdown.