Theoretically yes but usually they target distributors in preference to users. It's easier to get a verdict or judgment against the distributor because it avoids the question of "what is a copy" and how that applies to the digital space and also because people are less sympathetic to distributors. The thing with P2P applications is that everyone is also automatically a distributor.

Yes, it happens with other copywritten materials frequently.

Without a doubt. Remember the Anonymous guys arrested by doing DDoS: http://arstechnica.com/tech-policy/news/2011/01/two-real-gun...