I work on a team with 4 other people. I've known 3 of them for years and consider them to be friends. I have a tentative guest list (wedding isn't until Sept. 2012) and of course they are on it. I planned to invite the fourth coworker, because I think it would be rude to just invite the others, but he is an odd duck, to say the least.
This morning, he came over to my desk and said he had been thinking about something and wanted to share it with me. "I know you are planning a wedding and it's a small guest list, so I wanted you to know that you don't have to invite me, if you need the space for family or whatever." I was actually speechless. I finally managed to thank him for telling me that, and I had planned to invite coworkers A, B and C so of course I would invite him as well.
This is my first real awkward-guest moment ... I'm still kind of dumbstruck that he actually said this or was even thinking about it. I won't send out invitations for more than a year anyway. It was very strange!