Hasn't MS Word had a grammar check for 5 or 10 years already? Do other apps really need a grammar check? Seems like an odd one to bundle with an OS.
That is definitely a feature that would be nice to have when writing e-mails, posting on blogs, posting on forums, etc.
I still can't believe Windows doesn't have built-in inline spell checking so other apps can take advantage of it. This is 2007. Word has had the feature since what, Office 97? Maybe even Office 95?