Not sure how to explain this myself but I have seen influx of players with this. Not even downloading at full speed or having some packet loss can really make you warp so much that it makes it much harder for other players to hit you. There are many easy ways to do this including just spamming network cvars to the server.

How someone else put it: http://www.gamefaqs.com/boards/437678-/59897136
http://wiki.teamfortress.com/wiki/Hacking#Tapping_Hacks

The only major problem with this is it's not detectable and sometimes you can't tell the difference between legit lags and intentional ones. I have been using my piss poor connection for years and I never warp so much that it would give me an advantage

I heard it's a P2P problem, at the same time Steam seems to have fixed it in the latest update.