I would rather see the arrows fly in the regular Forum threads, instead of private barbs sent back and forth!
Since we have PM capability, I don't see the benefit of "chat", as both users must be on at the same time. Then again, while I only get on, read/respond, then leave when I am caught-up, maybe others keep it open and up, so they can see almost-real-time updates.
For me, no chat necessary. Others may see benefit.