The title is very much self explanatory. There's a lot of grief going on around the announcement of the PS4 that's related to this aspect of a console so I gotta ask: how much do you actually value backwards compatibility? Do you replay your previous gen games often enough that the feature would be a deal breaker for you?
Honestly, when I got the PS3 I was actually aiming for the PS2 compatible version. At the time I couldn't find it anywhere so had to settle for a 40Gb model. To my surprise though, I've only ever booted up the PS2 to replay some old games only half a dozen times at best in the past 5 years. PS 1 games? That's what the PSP is for in my opinion, since on the big screen they look like Hell.
While I expected the lack of that option to be grating, over time I came to the conclusion that I'm doing just fine without it. I don't even go back to some of the PS3 games that I own to replay.