From lurking, I believe we've reached the point where quite soon GPU won't be worthwhile at all. They have been surpassed by FPGA and now ASIC; the impact of those technologies' far greater hash rates will drive difficulty up. Of course GPU mining will still be possible, but due to the increased difficulty, it'll take a lot longer to mine coins with GPUs - and it's probably the case that the coins a GPU generates will be worth less in total than the electricity used. You would just lose money.