I'm a big fan of the MiFi devices.
I think it's a good idea having one, it's actually designed for tethering (mine is up to five connections).
A MiFi can be left upstairs to get better signal & you can be downstairs with your phone or laptop & you'll get internet. This is great for traveling or visiting the countryside where the gg 3g signal might not be so good.
Of all the people on here whining about tethering, a MiFi is good for that & it helps you out when the gg 3g signal is poor (mine is on 3).
It means you can keep your phone cheap, with a little bit of data. Use the MiFi for laptops & what not.