I've gone ahead and followed Jeremy's excellent iPhone Jailbreak instructions for one specific reason: the ability to install PdaNet on my iPhone for tethering. PdaNet let us know, along with reader Lawton, that they've given up waiting for App Store approval (which will likely never come anyway) and have gone ahead and released their application for jailbroken iPhones. You can get the full skinny here.
PdaNet for the iPhone is heads and shoulders above their other offerings in that it doesn't require any software on your laptop. You simply need to set up an 'ad hoc' WiFi network (here's how) on your laptop and then have your iPhone join that network. Then, boom, you're online.
PdaNet will also work in the background (yet another reason to Jailbreak -- real background apps), although they caution that you'll want to make sure that you get back into the app relatively quickly so it doesn't idle. They've also implemented another neat accelerometer-based feature: set your phone face-down and it will turn off the screen, saving power. Truth-be-told, though, you should probably leave it plugged in, an active 3G connection and WiFi connection isn't going to be very good to your battery.
One last note: over-usage of PdaNet's tethering is likely to draw the eye and the ire of AT&T, so use with care!
Thanks to Lawton for the tip!