I, for one can't wait for Battlefield Vietnam to come out. I plan on getting in line.
Since I only just discovered Battlefield at Christmas time, I play almost every day, should say night, at between 11 PM and 2 AM Central Time. Mostly Desert Combat though, it's just a lot more fun than regular BF 42, to me.
Also played the Eve of Destruction mod, which is based on Vietnam, but can't say I like it to much. The planes aren't as responsive and the helos are a lot harder to fly. May be realistic though.
From what I've read, the helo controls in DC are modded from the airplane controls and the new "Vietnam" helos will have there own controls, making them fly even more realistically.