I recently installed the DNG codec to preview my photos in Windows and I let Vista Search index all my storage. It was taking weeks and the number of indexed files was barely moving. I wasn't sure what it was so I started excluding folders from the index one by one. Eventually I realized that it was the Pictures folder which contains roughly 60GB of mixed JPG and DNG photos. I uninstalled the DNG Codec and now indexing is finished, including the Pictures folder, several hours later.
Vista Home Premium, 32-bit, 4GB RAM, Core 2 Duo 2.66MHz.