Do it. It works well. I've posted a couple of times on here about throwing in some War Weaver just for uber buffing power. Basically you want a +casting class to fill the gap between Bard 5 when you get 2nd level spells and level 10 when you have enough skills to get into Sublime Chord next level. (Unless you're a Savage Bard, it was pointed out to me, you can't go Bard 5 / Ur Priest because of the Fort requirement.) Personally I like Mindbender, War Weaver, more Bard (Bard 7 gets you third level spells, Bard 8 gets you Inspire courage +2, both good breaking points)... depends on what level you are already, how much farther you want to go just being a Bard, and so on, what break point works for you. Overall, I highly recommend Bard / Ur-Priest / Sublime Chord / Mystic Theurge very well.
