I'm OCD about a lot of things. Probably the biggest one is when it comes to professionalism, being spelling and grammar. I HATE when things that are published, e-mailed, printed without being proofread. I most especially hate it when it's me! I personally feel that spelling and grammar are easy to get a second opinion on before being sent, published, posted, etc.
Sometimes I get in a hurry and don't do it, then I notice it later and get all mad at myself. Especially, because I know how annoyed I get at others lack of spelling and grammar so I KNOW there are people that feel that about things I write.
Let's face it, if you want to be seen as unprofessional, it's easy to do and happens WAY too often. Let's proofread!