Agreed about the "worth it" factor.  In about 3 months the weather will start cooling off, so even if the difficulty rises over the summer in the fall/winter I have to heat the house anyways.  Granted that mining hardware is not as efficient as a heat pump, but at least the waste heat goes to use rather than running the air conditioning even more.  We'll see about next summer.  By then the Radeon 7xxx cards will be out and there will probably be FPGA/ASIC clusters online as well.  Having said all that, I still think we're quickly approaching the point (maybe 2-4 weeks away) where purchasing new hardware dedicated for mining will not be worth it other than for the "fun factor" to get a few bitcoins and join the community.