Determining hot items with exponentially decaying likes

Yes, that's exactly what this is doing :) But it's doing that in a specific way to keep the sort order equal to exponential decay, and make sure that the numbers don't cause floating point overflow and rounding errors.

Reddit does boost the score of newer posts. It doesn't do that for the value of votes though. Reddit simply adds the (scaled) timestamp when the post was created to the score of a post. This way newer posts get a higher score than old ones. Reference: http://www.outofscope.com/reddits-empire-no-longer-founded-o...