We do 1 point per 14 yards punt return and 1 point per 33 yards kick return. Return TDs are the same as rushing and pass-catching TDs.
We came up with these numbers for return yards because we wanted the average punt return to get about the same number of points as the average kick return, not including TDs, and that's how the 2009 numbers worked out across all 32 teams. For 2010, the numbers would work out so that we should've done 1 point per 14 punt return yards and 1 point per 32 kick return yards, but I forgot to fix it.
You could move both up or down in proportion and keep the average points per return equivalency, but we set ours so that both end up also being equivalent to the average number of points WRs get for the average passing attempt (and we give 1 point per 10 yards for receiving yards). Not sure why exactly we pin both return yards things to average yards per pass attempt, but doing it that way seems to result in a pretty good balance being struck between not having return yards turning a player who is normally nothing into a great fantasy player and making return yards something you have to think about.
Last year across all 32 teams the average kick return was 22.39 yards, the average punt return was 9.85 yards, and the average yards gained per pass attempt was 7.01.
I would be reluctant, as a commissioner, to use return yards at a website that did not allow differentiation of punt returns and kick returns (but I would still want return TDs at such a website). As compared to punt returns, your average kick return basically includes an automatic 18 or 19 yards.