Backwards compatibility is over-rated. Really, what PS2 games do you absolutely have to play?
The simple solution is to keep your PS2, it's not a sign of poverty to have a pre-generation console you know

. People who absolutely must have their PS2 games should own a PS2 and stop whining. If I had a Xbox game that I couldn't live without, I would not rely on it working on the 360.
My brother bought the slim, and it's a neat machine. Getting movie files to work is a pain, load times are a pain, exclusive titles are damn thin on the ground, and the online games are less regulated - but it's a good console.
The way I see it, you buy the console that plays the games you want to play, not the games that you already played through. The quality between the consoles is marginal, and it differs between games - I can't say which console has better graphics, because the graphics are different. The PS3 reminds me more of the GameCube than anything, even the PS2. It has these post processing features that I only saw anything like it on the GC. It's possible to get some gorgeous particle effects, and the refraction is just incredible. It really does boil down to what games you like though, Little Big Planet, Gran Tourismo and a handful of FPS games won't turn everyone's head.
I think people need to stop worrying about which is better, and try their best to buy all 3 major consoles. The PS3 and 360 are similar, but different, the Wii is unique, and has a footprint on the market, deep enough to bury anything.
Today, I will hopefully be buying Borderlands, on 360. I got L4D2 in the mail yesterday, and so am now patiently waiting on them to patch it - it's unplayable online as it is.