For me it depends entirely on exclusive titles, only reason I own a PS3 now.
If Final Fantasy versus XIII (or whatever they've renamed it to) and Last Guardian are now PS4 games as rumoured then I will likely get one at some point. If Naughty Dog continue the Uncharted series on it as well (and perhaps a Last of Us sequel) then that will certainly sway me.
Hopefully they have a stronger launch library than the PS3 did. It was incredibly weak in the beginning and combined with it's high price tag and being launched a year behind the 360 caused some pretty serious losses for Sony.
Whatever happens, new consoles means nicer looking PC games as they'll finally be caught up somewhat hardware-wise.