In reply to TobyA:
Typically, I find it starts to make a difference around the F7a/+ mark - it depends on the route, but that's normally the point at which I dig out my decent shoes. That's where the holds get poor enough to need better rubber, or a sharper edge, or the route is overhanging enough to need a more aggressive shoe, and where I need a shoe good for toe or heel hooking.
I don't have such a clear delineation for trad - I generally just use one pair of fairly decent shoes for everything (because I prefer lace-ups for trad, and only have two pairs of lace-ups vs lots of slippers/velcro), and normally only climb E2-3 max - which isn't really on ground equivalent to F7a.
Edit: I have heard - but can't remember or find the source - that many pro climbers get their shoes resoled if they don't like their sponsor's brand of rubber.
Post edited at 17:39