It's difficult to post comparable PC specs for the same reason that you can't compare iphones and android phones based on specs alone - it's a matter of specific hardware versus generalized hardware. When you know exactly what you're working with, you can get things running much more efficiently. That said...
Jaguar is a low-power architecture (think Intel's Atom). We don't know the PS4's clockspeed for sure, but if we assume it'll be somewhere in the 1.6-2.0ghz range, the CPU might be able to butt heads with a lower-end Core 2 Quad (2.4ghz or lower, probably).
On the GPU front, you're probably looking at something that, if it existed for the PC market, would slot in around a Radeon 7850 or 7870 (or on the Nvidia side, a GeForce 660 or 660ti).
Just as many games ran at 720p in this generation of consoles with some managing 1080p, I think we may still end up seeing a number of 720p games. Resolution increases take a good bit of GPU horsepower, so developers may or may not be able to have their cake and eat it, too - they may have to sacrifice some fancy shaders to get full 1080p going, or they may have to stay at 720p to get all the effects looking as nice as they want. We don't know yet, though - we might be lucky and get 1080p everything.
Again, a computer capable of equivalent graphics would require a bit beefier hardware, just because of the whole "we have to make this work on a million configurations instead of just one" thing. If you put yourself together a fairly good computer to use as a computer (console vs pc arguments tend to assume a gaming pc will only ever be used for games when pointing out the price difference), then drop in a $300 video card (this is what I consider the true cost of a gaming PC, since I need a good computer for my hobbies anyway), you'll have no problem being able to proclaim yourself a member of the PC gaming master race.
