Fee dynamics seems to come up over and over again in these discussions, with lots of talk and theorizing.
I hope some data on what is happening with fees right now might help, so I wrote another blog post (with graphs, which can't be done in a mailing list post):
We don’t need 100% full one megabyte blocks to start to learn about what is likely to happen as transaction volume rises and/or the one megabyte block size limit is raised.