I would wait for the 780 GTX, I think the price to performance ratio is better... And if it is going to be as expensive as the Titan, you can go for 2x 680 GTX - there will be a price drop (hopefully).
Eh, no new games coming anytime soon so I'd wait to compare the 7series to the Titan directly. The Titan is overkill for 99.8% of gamers anyway. Save your money.
A comment fom the 0.2% gamer I play at 1080P with a GTX 680 @1200MHz core clock (Asus DirectCUII Top) and when I max Battlefield 3 out I get framedrops down to 42 frames. I notice those frames drops and they bother me. So I lower the video setting (no AA f.e.) to get average frames of around 100 and frame drops down to around 70. When I wanted to max the game out, the next faster card from Nvidia would be the Titan. So I think the Titan is a realistic purchase option - apart from the price and if you do not have a 680 you could expand with a second 680 f.e..
If you factor in 4k gaming wouldnt a titan be better than a 780? It seems at that point muscle, even overpriced, would be needed. Question is will the titan drop in price when the 780 is released? That is what im hoping and some dont mind 30fps vs 2160p.