The P.I. I work for is pretty strict about certain cutoffs for the GRE, but once you're past that I don't think it matters as much. Research experiences definitely trump GRE scores though, as long as you get past the initial cutoff. I do know that our lab has come down to two equally qualified candidates for admission and ultimately the GRE score was the only deciding factor. That's probably not very common though, but I think with competitive programs like PhDs you just have to try and make your application as well-rounded as possible.