Very much a Marmite (Vegemite?) device aren't they?
I've heard there's someone who frequents these forums who's not a particularly big fan.
I think the reason being that they think it's hard enough to write one gripping/compelling beginning without setting yourself the arduous task of doing it twice. I tend to agree.
Confession time. First time I had a stab at a novel I started with a prologue not knowing what the general perception was. It was subsequently lost by drip-feeding its info into the main story as the redraft progressed and I felt the overall book benefited as a result.
However, I have read books that do have a prologue but can't recall their names off the top of my head - so they can obviously work if used properly in the right hands although I think they belong, by and large, to an earlier age.