I disagree with having developers do tech support. In fact I think it's insulting to those that are great at tech support. Tech support is a skill in itself, not just a place to let developers play.

If you really care about support, you'll have people with that expertise doing it.

Also, developing is really something where being in the zone gets the most productivity, and support is usually an intermittent and sporadic distraction, it can be a real productivity killer.

I see why people say this in pricinple, I just don't think it's a good idea in practice.