The New York Times had a piece on the MiFi, focused on Sprint’s rollout. The Times was mostly positive if a bit hyperoblic at points. In the comments, most of the people who had bought one seemed happy with the device.
I’m always amused by the no-data-limit extremists that appear on a MiFi comment thread. 5GB of data is a lot if you don’t treat it like it’s on a wired network. Read your e-mail (with limits on attachment download size), browse the web, stick to IM and you’ll be okay.