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I'm going with the 3G option.

Mostly because there are too many areas where wifi is not available. As noted in the earlier posts. There's no guarantee that tethering will work with an iPhone->iPad setup (plus I haven't jailbroken my iPhone).

While there is an added cost the device really does come into its own when you include 3G, without it,you're stuck at starbucks home or a few other locations that offer wifi.

Plus when I've traveled, the provided internet service has been suspect many times, having 3g ensures that I'll have internet service even if the restort/hotel's internet fails to work.
 
I'm going to go with the 3G because I like the knowing that I will then be able to access anything I need online just as easily as I do with my iPhone, which I have WiFi turned off on. I don't have WiFi on my laptop either, I have a 3G card for that too. At the time I got the laptop and moved into my current residence, the cost of getting internet service and setting up the WiFi was prohibitive and the 3G card was the alternative, since then, I've never had to worry about getting connected wherever I go since the card has gotten me connected. Once I get the iPad, the laptop will basically become a "desktop computer". Since it's Windows based that will only be until I get my iMac or MacBook and switch completely to Apple. I am expecting that the iPad will replace my laptop when on the go.
 
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