I realized that there's one major hangup for me, and that I could grumpily live with the rest (and perhaps even get used to it). If you're in a similar boat as me, please feel free to post your #1 complaint.
For me, it's the size that previously read messages take up. This causes a *lot* more scrolling than in the past, and also causes it hard to identify unread messages if one is scrolling quickly (because there's so much extra scrolling). Both are extreme annoyances. I should be able to see a maximal amount of user-driven content (ie messages) in a minimal amount of space.
I could probably get over the font issues and other complaints that I have, but the amount of scrolling is ridiculous. It's not unlike the bozos on usenet who quote a 5 page post before putting their little gem of one line wisdom at the end - you're hitting space bar, or spinning the scroll wheel for 5 minutes for not enough of a payoff.