In Windows 7 and Linux the built-in card "just works" and supports the "n" protocol too. The dangling dongle just to have WiFi isn't really the convenient alternative. If your WiFi card in the notebook is a half-size PCIe, you'd surely be better of replacing it.
I usually have a dongle for my wireless mouse anyway, so it doesn't bother me as much. I use the same dongle on my desktop (since it has no WiFi card). For some a WiFi dongle isn't too bad an alternative, as long as it's cost effective. $12 dongle vs $60 or whatever WiFi card.
