I thought I would make a quick post in case anyone else who happens upon my blog is having this issue:
I installed Snow Leopard last night and, ever since, my fonts in Safari have been incredibly whacky. I fixed the problem by, first, using fontbook's "resolve duplicates" function. That helped a little, but there were still some funny fonts so I manually went to my arial font (my default font) and looked at the preview in fontbook. Sure enough, there was a duplicate in that set and one of them was definitely NOT arial. I deleted it and everything is back to normal. So, if you are having a similar problem, check duplicates in your default fonts because that may be where your problem lies!