A girl has said that to me once and I basically said "no, that's stupid, let's work it out", and we broke up soon after (well, a couple months later). On the other hand, I have actually said this and basically meant "break up". So my experience has been uh, mixed at best?
I don't think it's the best idea if you want to salvage your relationship, but at the same time I'm sort of the guy that (by now) feels a relationship isn't really "salvageable", it either works or doesn't. Anyway, I do know people that have taken breaks and are back together now and happy (like Bernard Black apparently), so it's not like it's never worked and never ever will work.
But for what it's worth, if my girlfriend said something like that, I'd start looking for someone new. I guess it depends on how much you like her?
Jam it back in, in the dark.