I thought I would add some thoughts now that I have one semester left for my masters degree (hopefully two of them).
1. I am way dumber than I thought I was smart. Previous entries list my undergrad stats if you're interested. I have worked harder in the last sixteen months than I ever have, and have probably just begun to discover what I don't know.
2. Since I'm not on the PhD track I have enjoyed the lack of stress from prelims or qualifiers, and this has enabled me to do a lot of exploring and reflection on the vast subject of mathematics. I'm glad I've had that luxury. It's nice to see the landscape before picking a subject to dissect.
3. Grades are funny, and seem to have a much more (inflationary) subjective content in graduate classes. In an odd way this gives motivation to continue the struggle, as if the prof. is saying, "Hey, we know this is hard stuff, and that you are working hard. Even if you haven't done that great on performance measures, you should keep it up." Hopefully it isn't that I have someone paying the bill.
4. I haven't been on a thesis option, but that might have been a good idea. I did manage to do a topics/reading course with a prof. and went through the process of writing and rewriting a block of (relatively difficult at the time) problems/exercises to complete correctness. This was a great learning experience and I highly recommend it.