I haven't deleted index.dat in years, and yet I was so surprised that CCleaner only showed that 0.31 MB was used up. I was expecting something in the 500-600 MB range)
Have you tried Easy Cleaner's option for deleting Unnecessary files? I used to forget to clean my machine for two months. Then Easy Cleaner wound find up to 500 MB of junk files while CCleaner just 50-60MB of files.
