When I first went HD, I made the mistake of buying a 32" 4:3 SONY Wega HD.   Got the 622 hooked up to it, and sure enough, all Dish HD had black bar top and bottom, and any SD was a full rectangular of black bar.   I was so annoyed, that I brought it back in a day.   Darn thing weighed a ton, and it was a piece of work just physically returning it.   Eventually got a 34" 16x9 XBR CRT, and never looked back.   (Even though this baby is even heavier  

  )  
While I can handle left, right black bars (like right now, my son is watching the Grinch from ABC HD - and it has black bars), I could not stand a full rectangle of black wasting the screen.