Does Google use something like a spell checker? perhaps G uses the spell checker of Microsoft Word
They certainly do check spelling and grammar - they even score reading level, but I'm sure it's their own software, not Microsoft's.
How does Google evaluate the quality of a url or site?
That's been the big question here for the last four months. They appear to be using a lot of different signals, and then combining them in very complex ways. So for every person who is sure "it's all about THIS" there's another who says "I fixed that and it did me no good."