It amuses me a little bit that AT&T has still not enabled tethering for iPhones. My central argument is that just because iPhone users use more bandwidth on their phones does not necessarily imply that that "excess" usage would carry over to tethering. All AT&T has to do is price it they way they price tethering on other phones/devices. For instance, the Laptop Connect plan they offer on the USB dongles is either $35/mo for 200 MB, or $60/mo for 5 GB. If they priced tethering like this, then it wouldn't really matter that they used an iPhone or, like me, got a USB dongle.
I decided to go with an AT&T Quicksilver dongle. These are actually rebadged Option iCon 322s, so operationally they're equivalent. I was able to get it working 3 ways... Under VMWare Fusion with Windows XP, under Snow Leopard with their GlobeTrotter Connect software, and "semi natively" using the built-in networking.
If you just plug the Quicksilver into a mac without loading any drivers, nothing happens. If you then go and download the drivers that would appear to be the correct ones, you get mac kernel panics, which are otherwise known as the "grey screen of death." Not a good way to start. Googling around finally led me to relatively new Snow Leopard compatible drivers, which worked. With those drivers, and the GlobeTrotter software, I got a connection fairly quickly.
What's somewhat less wonderful about this is that behind the scenes, their software accomplishes this by setting up a whole new Networking "Location" with nothing but the laptop connect card in it. This can conceivably cause issues with VPN configurations. It would be much better in such circumstances to configure the network stack yourself. Fortunately, I found this blog post that has the instructions for setting it up.
As for the device itself, AT&T offers refurbished units free of charge with a 2 year contract. You can, instead, buy a new one for $99 and get a $100 mail-in rebate. For a device that is completely devoid of any user controls, I can't imagine why a refurbished unit wouldn't be perfectly acceptable as opposed to a new one.
The speed is just as good with each method. I was able to run some speed tests and got about a megabit up and down for the most part. The advantage of using the Globetrotter stuff is that you get a signal strength indicator. The advantage of using the control panel is being able to use a menu item icon to connect and disconnect, and potentially being more compatible with VPNs.
But potentially the best option is yet to come. I have a Netgear MBR624GU wireless router on order. If this combination works, then it will be the exact equivalent of a coffee house wifi hotspot that you can take with you anywhere you like. I'll revisit that topic when that device arrives in the mail.