I just purchased one from ebay for about $150. I've only had it a couple days, but i'm fairly impressed. the first thing to know is that this thing uses Sprint's 3G network. Anywhere you have Sprint's 3G network coverage, you'll be able to use this thing:

http://coverage.sprint.com/IMPACT.jsp?ECID=vanity:coverage

after you get this thing online, you have to set up a virgin broadband account. it will associate your mifi device with your account options. then, you have to pick a plan. they offer a 10 day, 100MegaByte plan for 10$ and a one month, unlimited data plan for 40$.

the 10 day plan doesn't do any type of rollover. it's 100MB or 10 days, whichever comes first. i like this plan because it beats the pants off the 10 dollar for a few hours that you pay at airports or other paid hotspots.

in my limited testing, i observed speeds at 100KBps and above. that's not too bad in my book. you can get the theoretical caps looking at the link below:

http://shop.sprint.com/en/stores/popups/compare_data_speeds_popup.shtml

overall, i'm very impressed. the fact that it's "no contract" is the best part about the service. and it's reasonably priced.