Yeah the only problem with flash upload for classifieds would be the way things are handled is it theoretically possible. See in the gallery which has a flash uploader each and every image you upload is a photo in the gallery and processed as such.
I do not see how the flash uploader would work in classifieds just because image uploading is secondary in those applications. You can have up to 9 images for each ad. If you allow mass upload the 6 million dollar question would be to how to dissallow any image uploads after the 9 max for that ad is reached so one can continue on with the ad submission.