Vita is really trending down dangerously. With nothing noteworthy at all in the horizon, and probably the only worthwhile title coming out anytime remotely soon being Persona 4 Golden... it's not going to be good for Sony at all.
By my reckoning, if there's no change to their relative selling amounts, the PSVita LTD will overtake the 360's LTD in about 77 weeks. Now, I expect some fluctuations there - I'm sure PSVita will be boosted more by holidays than the 360s, but I also expect Vita to drop lower than the current position at times.
My random musings: Can Vita overtake the 360 before the 720 comes out?
(Not a stat that particularly *means* anything, I hasten to add! Just something that struck me as possibly quite close)