The compute capability isn't a huge issue for us.
NVIDIA just released the new Tesla line (with the new architecture and thus the highest compute capability), and @xchoo is right: They're a lot more expensive for similar performance (in terms of FLOPS and memory bandwidth):
So what does the Tesla line get you? Here's a good summary:
A few of the key features, like better double precision performance and error correction, are things we don't really care about. And I think even if the Teslas last longer, you'd still be better off buying something from the GeForce line once every couple years for \$500-\$1000 (and I think they can last much longer than a couple years unless you're using them non-stop), than buying a Tesla once every 5-10 years for \$4000-\$8000. Not only is GeForce more cost-effective, you'll get better technology by being able to upgrade them.
My takeaway is that Tesla is for servers that need great reliability in their GPUs over long periods. As long as whatever's running on your GPU is not mission-critical (and for anything we do it's not), then you don't need a Tesla. If you've got the cash, save your money and hire more people to do research instead.