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..