Console design, look and reliability (even though I'm on my third I'm mature enough to know I'm unlucky and the damn thing is still more reliable that 360, although I'm sure the Wii is most reliable of all given its nature)
BC for PS2 (for me anyway, I know this is gone for many now) and up-scaling of PS2 games
Strong 1st/2nd party exclusives
Decent mutli-platform library
Quality of PSN games like Warhawk, Flow, Pixel Junk Eden, Super Stardust, etc.
BR & DVD up-scaling
Strong multi-media support for photos, music, videos. I now have all my digital photos & videos on PS3 and streaming music from my PC.
I want to play LBP more than any other game at the moment and its on PS3
I'm also interested in PlayTV and PSP hookup - although I'm unhappy that the PSP elements may have been removed. I'll need to watch how that develops.
With my Wii and PC it fills out all my gaming / multi-media needs nicely.
Try to be reasonable... its easier than you think...