I'd say that if you want one, to go ahead and get it. Given Sony's recent systems and a lack of backwards compatibility (PS3 removing PS2, Vita not having any way to port PSP UMDs), there's a good chance that the PS4 would still not even open up the library of PS3 games that interest you. And to echo with the choir, there is a chance that Sony may drop the PS3's price later this year. I'm skeptical of it, personally (I think that Sony still wants to remove some of the red ink from early in the PS3's life and the recent hacks.), but it's not something that can be completely ruled out.
Ironically, the only systems I would make an argument for holding off on are Nintendo's. The Wii has its successor next year, and the only thing being dropped there is support for Gamecube. And the DSi family has been made obsolete by the 3DS. Anything else, well... I really can't make the argument to not buy if it has games you want. So I'll reiterate: go for it.
-dunno001
-On a quest for the truly perfect game; I don't think it exists...
