Stuff stuck to edge of bottle

[MontereyRick]

Can someone answer a question I've for a while now...????

On numerous occasions I've had a bottle of Cab/Merlot which, for all intents, tasted fine but upon emptying most of the way noticed that there was some kind of residue/skin/glop(for lack of a better term) stuck to the side of the bottle.

This residue has been as small as a quarter or as big as 2"x2". I've had it in brand new bottles, some cheap and some pretty high end (most recently had it in a bottle of Marquis Philips S2 Cab 2001). The Wine has generally tasted fine and didn't seem corked or tainted in any way.

What is it? Is it a sign of something wrong with that particular bottle that would steer you away from buying or drinking it or what? Does anyone know what I'm talking about?