As of today (April 6, 2013) mining profitability on GPUs is at the highest levels ever, but that is only because the exchange rate has rocketed up so fast.
At the same time, mining difficulty has been skyrocketing and that pace of growth will likely outpace the increase in the exchange rate.
But there are probably two or three difficulty adjustment cycles remaining where mining bitcoins using GPUs is still profitable. Enjoy it while it lasts because in a little over a month it should be all over for GPUs. The expected rate of difficulty increase was not unexpected so further investment in GPU mining has been discouraged however the rise in the BTC/USD from the low teens to 10X that level has caused that call to be simply premature by a few months.