I don't have any problems with the HR34. I have 3 h25 boxes with it though, which are HD boxes, non DVR, but they have their own tuners. That way, I have no recording conflicts, and the H25's can access the HR34 DVR, set up and watch recordings.
The only downfall with the H25's is that you can't just pause and rewind live T.V. with them. If you want that ability, you just hit record, then pull up the program from your list of recorded programs, and now you can pause and rewind. For my house the benefit of them having their own tuners, instead of it taking one from the HR34, is the much better setup.
I don't have any problems with my HR34 and switching channels. It is just as responsive as my 722 with Dish was. It didn't record a show that it was supposed to, but that was about 3 months ago. I reset the box, and haven't had any problems since.