I have no real figures to give you, but I wirelessly tethered my droid last night, and then had my wife use the computer for general browsing. She didn't notice any difference vs the Comcast/wireless router we have set up. Now I admit she didn't do anything graphically intensive like videos. Downloading files are definitely slower, but for general browsing and forum reading, it works quite well.
You can't "legally" tether but a bunch of people are doing it anyways. I tried it but it was too low for playing games with. Got 0.70 download and 0.20 upload speed. It's okay for browsing, but that's not what I need it for. Hopefully it connects faster if I get the $60 mobile broadband plan.
