OK there is a really useful extension available for free to VS.NET 2010 named "Spell Checker". It shows misspelled words within commented sections with the traditional red squiggly line under the word as seen in Office products. Obviously correctly spelled words are not critical to an applications performance, but well formed internal documentation that reads well such as commenting is important.
You can download it for free by going to Tools -> Extension Manager and then select 'Online Gallery' from the left-hand side. In the search box type in the top-right hand corner, type in "spell checker" and search. The 1st extension created by Roman Golovin and Michael Lehenl (thank you) named "Spell Checker" is the one to download and install (shown below).
As you can see below, just hover the mouse over the misspelled word for the little box to display, which upon clicking will bring up the properly spelled words. There is also the ability to "Add to dictionary" which is nice, because often many words we use are technical and not in the dictionary.
It can also be downloaded directly from the link below:
Spell Checker Extension for VS.NET