That's a good find. It happens for me just as you described. I'll post it on MacFixIt ASAP, and hopefully readers can help confirm it and send bug reports to Apple.
Snow Leopard's Preview can no longer do a search for dollar amounts accurately. This worked just fine in Leopard, but no longer works in Snow Leopard. Go ahead and download a PDF of your most recent bank statement, or any PDF that has a bunch of dollar amounts in it. Then, do a find for one of the dollar amounts. For example, do a find for: 50.00
Preview will no longer find a match for 50.00... instead, it will find any instance of "50" or "00" in your entire PDF file. It uses the decimal point as some sort of a delimiter, and it makes Preview believe that you are doing 2 completely separate searches.