Leaf, t doesn't bother me to keep track, it frees my mind...
Mike, MS Excel is what I use, one column per site, the first three ones being for the file name, the title, and the thumbnail which I copy from one of the site and reduce to fit.
In each box I put the site file number (if any), the date submitted, the result date with any useful comments given from the site regarding the picture. Plus a color code for the practical visual aspect: blank for waiting, yellow for approved, grey for refused, and green for deleted by myself. I also use bars to differentiate the dates submitted.
I find this system very practical. This way, I don't have to think too much about what I did with what and with who, just entering the new info and go on shooting

Have fun with whatever you choose!