I'm inclined to disbelieve the contamination risk theory, because it seems like the risk would be the same as it would with new yeast fresh from the store.
As far as mutation goes, what should I expect? If it keeps creating tasty homebrew, I don't really mind if it's not the same from batch to batch, but if it becomes an undrinkable abomination, that's another story.
Anyhow, I brewed The Innkeeper (Wyeast 1469 PC West Yorkshire Ale, OG: 1.043), then repitched into Spiced Winter Ale (OG: 1.047), then repitched into Shirley Furioso (OG: 1.062). My plan is to keep repitching for as long as I can (read: I end up with undrinkable or unfermented beer).
The first two times, I just poured the new wort right on to the yeast cake after I racked the previous beer into secondary, and the third time, I saved the yeast cake from the primary in an erlenmeyer flask, and refrigerated for a few days. So far, everything's been going great. I'm considering washing the yeast this next time, since I'm sure the trub has been building up.
Thoughts, suggestions, concerns, advice?
Secondary: Synchronicity Wheat, Cider, Wildflower Mead (1 year)
Up next: Caribou Slobber