I have it set to 125%. I have a high-DPI display (the Apple CinemaDisplay 30"), and I like to sit about two and a half to three feet from the screen. Any closer, and I would eventually go blind of excessive nearsightedness. Additionally, I like the smooth crispness that fonts take on when they are at a higher DPI. Less apparent aliasing (even with anti-aliasing on, you can still see some slight stepping at 100%.)
I truly can't wait for higher DPI screens, though. Now that Windows 7 has support for very high DPI, I would really pay to have a 30" WHUXGA 7680×4800 pixel screen. Thats three times as dense as the 2560x1600 pixel resolution of 30" screens today, or 300dpi. Fonts at 125% would truly be a dream (and it would be a photographer who creates his own prints holy grail.)
Sta.sh
Devious Comments
I truly can't wait for higher DPI screens, though. Now that Windows 7 has support for very high DPI, I would really pay to have a 30" WHUXGA 7680×4800 pixel screen. Thats three times as dense as the 2560x1600 pixel resolution of 30" screens today, or 300dpi. Fonts at 125% would truly be a dream (and it would be a photographer who creates his own prints holy grail.)
I'll buy a PC when back to Portugal