The problem is the "old" forum style uses a mix of relative font sizes and fixed font sizes... the poster's name and what not is specified in a semi-fixed font size and appears erratically in size depending on your browser and other Windows settings.

I'm trying to switch to completely relative sizes, so that everything can be easier shrunk/enlarged by the user. Sizing stuff like this can be tricky (it's SO much easier when I just specify an exact size).

I've played around with the sizing of those items, let me know.

As for body text, it's only slightly larger than before, but it's a wider font that may "appear" bigger. But as Greg says, it's quite easy to shrink things. You're just used to websites that still specify font sizes ideal for 640x480 monitors! :-)