My first thoughts about T-Mobile's 3G card for USA are ... this.
1) No Mac support yet. But it is coming they promise.
2) Coverage area-very spotty so far, at least in San Diego County
3) Easy to install software for PCs. Installed quickly and fired up without issue on my Asus 1000HE Netbook. The software comes pre-loaded on the USB sitck.
Small, light. Made by Huawai, so the software for Macs won't be hard to write, as already 3 in the UK has that up and being offered.
More to come..
Update-I was at San Diego International Airport and ran a speed test. I was underwhelmed. I'm used to seeing speeds in the 1-1.5 range these days on 3G or even in the high hundreds. What I saw was sub 500K down and under 200k up. That's not what we should be seeing on a network that has such a small number of users. Maybe it was the location?