The backward compatible issue is a non-event. The only PS2 games I have left are dance and karaoke games that others in my household play. I generally don't keep games. I buy them, finish them, and move on to the next one...
If the PS3 was pretty certain to be a $399 console come March of next year, then I would wait. LBP and Killzone 2 are the two games I'm most looking forward two and they are listed as Feb. 08. If they slip like so many have recently, I'll be right there in March...