Its not gonna be the best option for gaming and super smooth browsing. It is the cheaper alternative that saves you some money.
[Video] 20+ of the best android games on the Nook Color - xda-developers
Check that link out, it has a video of a lot of games being played. All on CM7, depending on the ROM/Android version you go with, yiour results will vary. You can see from that vid that the majority of current games are pretty smooth, still a bit jittery here and there.
You can always buy one, root it, test it, and if you dont like it, return it.