My MT4G using HSPA+ battery didn't do very well but, I had it plugged to the car charger whenever I went somewhere so, that helped. I could basically get through the day, with moderate use but, I had better remember to put it on the charger before I went to bed.
Unlike the Iphone, which could be at around 80% when I go to bed and, still at around 78-80% when I woke up; the Mytouch would be at around 15%
I would say if your a power user, to keep a car charger around and, use it when traveling somewhere. It would also be good to have another charger with you, in the office, at work or wherever you are. It kind of sucks but, that's the way it is. The thing I like about the Xoom's charger is, it charges rapidly (both the car and dock).