Estimating file download time

Bram Cohen (the BitTorrent creator) has posed an issue with estimating download times for files. Bram writes

"It turns out that estimating time left to complete a download is non-trivial. What BitTorrent currently does (simplifying a little) is to average total download over total time for the first half of the file, then for the second half of the file to update estimated time left as each piece comes in by assuming that the amount of download averaged over for the current estimate is equal to the amount of download left. This approach gives a fairly reasonable estimated time left under almost all circumstances, but it has a significant artifact."

There are a few approaches suggested in the comments on the post. Whenver I have faced the same problem in the past, I applied this 'trivial' work around- estimate the time left with current download speed and remaining file length - a reasonable approach I guess. Lets see if Bram proposes something easy to follow.