I agree about not forming a team with friends, but I would tack a couple of things onto that:
- Doing (short) game jams with friends is actually a very nice way to get into jamming and learn together, since you already know your team-mates well and the project has a very short timeframe
- Likewise, comparing notes / sharing progress casually with friends who are working on other game projects can be (from my experience anyway) a very good source of motivation