I use iTunes now only because I run both an iPod and iPod Touch, otherwise I'd be back to using the MPC as well.
My only complaint with MPC was playing DVDs; when you browse menus in fullscreen the menu options move but the place you have to click to select the options doesn't move with it, so it's a bit of "move your mouse around the screen until the menu button lights up and hope it stays lit up while you click." Otherwise, great.