It looks like the font for the message area has recently changed. I find it a little harder to read, it seems a little smaller and isn't always rendering as cleanly (in FireFox, anyways). It's hard to find an example, the closest I could find is the second "t" in "Chatter" near the top of the attached image.

Alignment of some elements is off as well. When reading a message, all of the header captions except Forum and Category are vertically misaligned with respect to the field contents (as shown in the image). Maybe this is a side effect of the font change (?)