A new set of speed-running ladders have been added to Doom2.net, and I'm pretty sure the Bahdko can explain the concept much more eloquently than I, so here's her email on the topic:
In addition to the Combat-Shotgun competition ladder that was released last year, there are now three speedrunning ladders. They use e2m5, e1m3, and Doom2 Map02 in -nomonsters mode. The rankings on the ladder are determined by the exact demo times, which is into the hundredths of a second (or in gametics, actually). The main site for the competition ladders is here.
A note about competition ladders: A competition ladder differs from the more common tournament-style competitions such as Compet-N in that it is a structured list of players who are competing against one another for ranking on the ladder. The participants are not necessarily competing for the top position, and in this kind of single-player based ladder, they do not have to schedule matches with other players like in the older, BBS-style ladders. Participants record and upload faster recordings whenever they feel like it, essentially.
Directions on how to participate are linked from the main ladder page, for anyone who's interested.
--Bahdko (the proud occupant of the bottom rung of the speed ladders.... woo ... admire the skill, yeah, not).
Remember: don't admire the skill.