Windows 7 on my netbook, Ubuntu on my laptop, XP on my desktop.
IDE_0018 is useable on windows 7 but 1.0.1 is laboriously slow on win7
funny though 1.0.1 is pretty nippy on Ubuntu
for years i was using win 98se and had no hassle at all,
XP is good all round for the Arduino, PIC & Nintendo Gameboy programming i do