A lot of people are using this on their fuzzing rigs with large software applications like Firefox. ASAN hugely decreases cost per test cycle (and therefore cost per bug, without changing fuzzers).
A friend and I chipped in to get a fuzz server (quad xeon X5660, 96 GB RAM, dual SSD). It's paid for itself twice over in bug bounties and there are more in the queue. Valgrind was always too expensive but using ASAN builds we can find more bugs.
Having ASAN support in GCC would be really handy, because for large projects it can be a major effort to get everything to compile in CLANG.
If you are sufficiently paranoid, and willing to accept a speed and memory hit (roughly factor of two) you could use ASAN in production. Personally, I am beginning to entertain the idea of using an ASAN-instrumented browser for day-to-day use.
That's a pretty interesting idea, and seems to be a practical realization of something people have been trying to do for ages: produce a C variant with more safety. The most prominent project I know trying to do that is the C-like language Cyclone (http://cyclone.thelanguage.org/), but this seems like an alternate approach that lets you get "C but safer" without actually moving away from C.
Cyclone is something every programming language enthusiast should look into, IMHO. It's extremely interesting, well-done work.