I do feel the 30D is a superior camera despite the 400D having more megapixels.
The truth is that there is not a huge difference between 8.2 and 10.1 megapixels. Much more importantly both have very good low noise levels at high ISO settings, both have very good (top of the class!) autofocus, etc.
The 30D basically shares the 20D's autofocus with a few minor improvements, and the 400D gets that from the 30D.
However from what I've seen since owning one, 30D's body is superior (handling, durability and grip for most people), viewfinder brighter & larger, supports a few more features (faster burst rate, 3200 ISO and spot metering).
So I would not go on megapixels alone. In fact that is one of the LEAST important features of a camera to me.
For me, the 400D is an attractive entry level DSLR camera because of the bigger screen and the dust-removal system. (however I've never had a big problem with dust!) but I also like having 3200 ISO and that wonderful wheel on the back, which only the 30D has. I also hate the smaller look DSLRs.
It would be nice if the 30D had the 10mp but canon couldn't do it without increasing noise or affecting buffer depth and shot speed, and 8->10 is more of a marketing feature than a true step up in resolution.
They judged that 30D users would rather have a deeper buffer, 5fps and high-ISO performance than a few extra pixels.
so you have to way up what your needs are and they are both great cameras