I certainly believe Sony can be competitive next generation, but only if they do most things right.
The biggest problem I can see for Sony now is the damage done to the product name. Despite the crazy starting price it was the Sony name and the Sony faithful that allowed the PS3 to get rolling in spite of the $600 price tag. That simply isn't going to work again, they're going to need a really good console at a really competitive price, with good Sony-exclusive content that's not too far behind the competition in terms of release.
Having said that I don't think that Sony is in a position to play the ace that is required for them to get back on top. As I see it they aren't in a position where the can play the technical arms race with MS or the creativity game with Nintendo; they don't have the money for the former and can't afford the risk on the latter.
Company-wide financial issues have hamstrung the gaming division to an extent that they can no longer follow the strategy that brought them to dominance in previous generations and they are now facing significantly more mature competition.