After about a month's use I can safely say my phone has yet to fully drain.
I do charge every night, and often the charge floats around 50% after a full day's use. I surf quite a bit (on wifi), play some games, etc. I admit though, that since getting Mango my Omnia doesn't grab 3G as often as it used to (it's usually on EDGE). This is a known issue with Mango, so I'm sure I'd see heavier drain if I was on 3G all the time.
Since I bought the Mugen day one, I can't really compare it to the stock battery. I too, would be curious about WP Bench drain tests. If I have some time where I don't need my phone, I'll try it out.