do it occasionally. Mostly try to pick a MTB bus or something similar large and bulky. they're take a bit longer to get up to speed and are more gradual stopping. Plus the sheer size means you don;t have to hang on the bumper to get a good draft. All adds up to a bit more follow distance. All the buses here in the valley run in Nat Gas and the exhausts are up high. I try to hang at the left side, so the driver can spot me in his mirror, for no other reason than to let him know I'm back there - not expecting him to do anything out of the ordinary. Very occasionally I'll get a quick wave as I go by, when the bus is making a stop; but usually nothing. They've all been cool about it, to date.
Its a lot more fun and a bit easier these days, since I've gotten a bit more snap back into the legs.

UPS trucks? Never thought of it. They all drive very quickly here...
The buses usually motor at 35 to 40 mph, the UPS trucks and other traffic rarely are under 40 mph, and jackrabbit the lights. The only time traffic flows at less than that is in SB City, and it just ain't worth jumping on for just a block or 2.
Private vehicles and non-pro drivers - way toooo spooky
There are a bunch of Nuevo scooter riders around here these days, but they're all so 'newbie' that pacing behind them would be a frightening experience for both parties.