I consider my spelling and grammar to be quite good (oops.) But I am not an expert by any means, having absorbed the rules of grammar mostly by osmosis from massive reading. I couldn't tell you what a subjunctive was if you paid me.

I do tend to be a bit anal about spelling, and have found myself correcting spelling errors in other people's stuff when I quote it.

I'm also irritated by certain dumb errors that I see a lot from newspapers and others who should know better (read this morning about "hoards" of people.) I fear that as more institutions rely on spellchecking software, much of which is useless in applying context, this is going to get worse.

I still find nothing more useful in checking a document's grammar than actually reading it out loud for flow.