Pay the same $1,000 for a GeForce GTX 690 if you only want one dual-slot card and your case accommodates the long board. It remains the fastest graphics solution weve ever tested, so there's no real reason not to favor it over Titan.
The Titan isnt worth $600 more than a Radeon HD 7970 GHz Edition. Two of AMDs cards are going to be faster and cost less. Of course, theyre also distractingly loud when you hit them with a demanding load. Make sure you have room for two dual-slot cards with one vacant space between them. Typically, I frown on such inelegance, but more speed for $200 less could be worth the trade-off in a roomy case.
Buy a GeForce GTX Titan when you want the fastest gaming experience possible from a mini-ITX machine like Falcon Northwests Tiki or iBuyPowers Revolt. A 690 isnt practical due to its length, power requirements, and axial-flow fan.
Buy a GeForce GTX Titan if you have a trio of 1920x1080/2560x1440/2560x1600 screens and fully intend to use two or three cards in SLI. In the most demanding titles, two GK110s scale much more linearly than four GK104s (dual GeForce GTX 690s). Three Titan cards are just Ludicrous Gibs!