I used the virgin mobile mifi just shy of a month before returning it.
The reception was fine everywhere I took it, but I found it to be too slow for my Netflix streaming needs. I have a 3G 16G and found AT&T's service to be a bit faster, but unless you were grandfathered into the $30/mo unlimited plan (which ends the moment you stop service), the average person will blast through 2 gigs of data rather quickly if streaming video; ie. Netflix, YouTube, Pandora, etc. - for that reason I did like the unlimited aspect of Virgin's mifi for only a difference of $15, plus I could use it with other devices, like my iPod touch, my Mac, or PC.
I currently use a Clear iSpot, which is a little thicker than the Virgin Mobile mifi, but delivers 4G speed, unlimited, for the same $25/mo I was paying AT&T - and best of all, there's no contract, just like Virgin's mifi.
For those who don't exclusively live/work/play in a 4G area, there's the Clear 4G/3G combo personal router that runs $55/mo.
The routers start at $99, but Clear runs specials from tome to time. I picked up my iSpot for $20. A bargain considering Virgin charges $150 for theirs, and Verizon charges $269 for contract free operation- neither matching Clear's 4G 6 Mbps download speeds.
If you're not in a current or future Clear 4G area, I would say that Virgin's mifi is the next best choice for the average ipad user based on it's unlimited data/no contract use.