Well, I handed my invites over to the USPS today. I decided to not go with hand cancelling... and I hope I don't end up regretting it.
I'm totally scared now. My cousin who is getting married on October 2nd just told me that 7 people still haven't received her invites, and she sent them a month ago!
I spoke with 5 different post offices about hand cancelling. Two of them refuse to do it at all. Two others said that they will do it, but that the invites would still go through the stamp cancelling machine anyway. The fifth one, the downtown (Center City or something like that) post office, was actually the nicest and msot helpful. He explained to me why it wouldn't matter if I had them hand cancelled. He said that with all of the machines they have now, there's no way to keep them seperate, and that they would indeed go through the machine anyway.
But, because he was so nice and actually took time to explain things to me, and was pleasant about it, that's where I took them and that's probably where I will take all of my mail from now on.
So, for any of you (especially if you live in Oklahoma City, apparently) who haven't sent invites yet and are wondering about hand cancelling, be sure to ask if they will go through the machine anyway.