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Some downsides to the Sprint Overdrive:

It's quite large and twice the weight of the mifi. Too big for a shirt pocket.
LONG boot times (a minute and a half) versus almost half a minute on the mifi. You won't be whipping this out and causally using it like a 3g iPad or even a mifi for that matter.
Recorded usage temperature is ~106 degrees.
Power HOG. 2 hour real world battery life, drains power quite quickly when charging via usb port, barely charges even when plugged into the wall unless turned off.

That said, I just started using mine. I'll give it a full 30 day runthrough before I decide if I want to kick out my mifi for this.
 
I do not want another contract. I wouldn't even get the 3G iPad if I didn't have a choice. I probably won't even activate the 3G until later this summer. I like the way they handled it a lot. If it has to be AT&T at least it is reasonably priced, no contract, and uncapped.

and IMO worst downside of Overdrive is battery life is like 3 hours.
 
Ok, just as another data point...

Buddy of mine picked up an overdrive unit last weekend. He let me borrow it today to try out here at my office (aka, the AT&T dead zone). I have it set up next to the window in my office and it's getting 4G signal. Hooked my macbook up to it and did a speed test - 3Mb down, 1MB up. WAY more stable and way faster than the 3G AT&T signal I get here at the office...

I'm pretty much sold on getting one in late June when the 2 yr contract on my AT&T 3G dongle expires.

1 Overdrive, service is about what I'm paying now, and I'll be able to drive the iPhone, iPad and Macbook all simultaneously, with better signal. And I can always pop on the 3G on the AT&T if needed...
 
I will be trying the Virgin Mobile Broadband adapter with the cradlepoint PHS-500.

No contracts and several devices can connect.

Coverage is not as good but still a good alternative if you don't want the iPad 3G.
 
Overall, it looks like the 3G option will cost you less in the long run ;)
That's probably true but then you lose versatility. By using another data plan (pre-paid or by contract) you can have more that just the iPad connect to broadband. Also keep in mind that as long as the iPad is running WiFi, all 3G restrictions are mute (skype calls and things like that).
 
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