You forget, negative results count in science too. Even if Seti@Home firmly establishes that all the radio noise on whatever frequencies they're scanning is meaningless noise, this at least gives us some firm lower bounds regarding the probable distribution of technological civilizations.
I personally doubt they'll find anything. The timescales involved are too great for it to be likely that there's anything within a million years of us in this half of the galaxy. But the only reason I have to think that is a moderately pessimistic intuit of some of the terms of the Drake equation. Hard numbers are NEVER a bad thing, especially when they can be obtained at negligible cost, like what Seti@Home is doing.
It's probably a good idea to try to work out, in a quantitative way, just how nervous the Great Filter Paradox should be making us. :)
Whistling in the dark...