I haven't found the resume function to be completly lacking, but certainly far less effective than one might hope it would be.

I would suggest, however, that if the resume capability were overhauled, it would be top priority to check for other possible download locations, even if the old one is still there. Perhaps even have a feature so you could click on a download and say 'check for other sources' or something, in case more people show up with your file during the wait for it to download.