I wouldn't suggest trying this without an appropriate data plan, but Dell Streak user Grayharley is almost two weeks into his 30-day experiment of using the device as his sole internet connection at home to see if he can eventually cancel his cable internet service.
The Streak is at the heart of a WiFi hotspot he's got set up at home, but he's not using Wireless Tether or Barnacle WiFi Tether (apps that turn rooted Android phones into free wireless hotspots) to do it. Instead, he's using PdaNet (no root required) to tether the Streak to his laptop via USB. Then he's connecting his laptop to a standard Linksys router, which is using the Streak's data connection and sharing it with all the other devices in the house.
To set it up, all he did was unplug the cable modem from the router, tether the Streak to his laptop, and go into the computer's network connections settings where he right-clicked on PdaNet, and clicked Properties -> Share -> Share using my wireless connection. Then he reconnected the laptop to the router (not using DHCP) and was done.
He says that while video streaming sites like Hulu and Netflix aren't as reliable as they are over cable modem WiFi, everything else is working extremely well. The connection is consistent/reliable and the Streak stays cools, even when left on overnight.
I don't know how often the Streak is untethered for use as a standalone device or whether it's ever used as a phone, but I'm going to keep an eye on Gray's progress. I have a friend who canceled his cable service in favor of Hulu and a Slingbox set up at his parents' house, but I don't know anyone who gave up cable internet for tethered 3G.[Grayharley.com] Thanks, Dave!