TF2: High ping-like lag in game, but my ping is fine!
its frustrating as hell. cant change weapons. movement is seizure-like/inducing. no ping issues. unable to type any text. limited use of voice chat.
ive gone over the networking, investigating paths to various servers. all seem fine. im using the same ISP as the OP in the thread linked above.
ive poked around at the network stuff with hping and bmon and a few other tools -- i think something may possibly be setting off some sort of rate shape on the ISP side, but no way of being sure. of course, you call support, they are about as intelligent as "the hordes" and claim all is well (they wouldnt know anyways, take if from someone that knows their support structure).

big clue to this being a steam-related issue -- started happening directly after a steam platform update. go valve.