I gave up my FPGA project - even if it's cheaper than ASICminer - because at current difficulty (and difficulty increase rate) the ROI rised to 6-8 or even more months. I have better investments than that :/ I'll leave these two PCBs I already made running and forget the whole thing.
6-8 months is a great ROI, actually...
what could possibly yield you better results?
the point is to make profit, not to make roi, making only roi is useless
and when i say profit, i mean an amount equal to the one invested, aka ROI X 2 minimum