I had no problems uploading a credit card receipt with Safari...worked like a charm. I am using the new Safari 3.0.2 so I don't know if this makes a difference or not. Apple claims Safari 3 is now the fastest browser on both Mac and Windoze.
jdec141, as far as your scans go, you might try tinkering with your scanner settings because my 200 dpi scan to jpg came out to be about 175k. When scanned to tiff it was 650k. Look to see if you're scanning an "image" versus an OCR document...different scanners use different terminology so your mileage may vary...but your file sizes definitely do not have to be so large.