I installed Snow Leopard last week, and I just noticed this problem a few minutes ago. The capital letter M has been replaced by a capital J in some places.
I was using Word 2008, and it unexpectedly quit. Which happens a lot with Word regardless of the OS.

I noticed that the letter "M" had been replaced with a "J" in the box that came up to send a report to Microsoft. There was a "Send" button and a "Don't Send" button, as well as one that said "More Information." Except it said "J ore Information."
I also noticed the same thing when I took a screenshot of this box and tried to save it with a filename that included a capital M. When I typed a capital M, it came out as a capital J in the text field for the filename. It took a lowercase m, but not a capital.
I was in Yahoo! mail and the title of my page had the same problem.
Then I saw the same thing in the page heading on this site. Instead of saying "Mac Forums," it says "J ac Forums," and it looks like there's a space between the J and the ac. Probably because capital Ms are wide.
I tried uploading screenshots to photobucket to link here, but it wouldn't let me. And in the heading for the pop-up window to Manage Attachments on these forums, the M in Manage was a J.
It only seems to happen with page titles and buttons to click. Has anyone else had this problem?