[antisthenes]

Personal reasons for upgrading to 7 in order of importance:

64-bit memory space support (crucial, considering enormous browser bloat after the FF 3.5 era)

TRIM support for SSDs (I switched to 7 when consumer SSDs started to become affordable)

DX11+ for gaming (DX10 was a wash in Vista, but by the time I switched to 7, there were some games that actually did look noticeably better with DX11)

Half-Open connection fix for torrenting.

But I'm a power user, so reasons for regular users may vary.