Regarding the capacity question, it really depends on what I end up using an iPad for.
In my mind, the biggest potential for the iPad is revolutionizing the way we consume print media, specifically newspapers and magazines. I would love to be able to download digital versions of magazines like Sports Illustrated, This Old House, etc. that include multimedia and interactivity.
I'd also love to load my entire photo collection on an iPad and have it available to show people.
If I were to buy one today, I'd probably go for the 64GB wi-fi only version, but I suspect I'll wait a year or so and get a much larger capacity second-generation version that could potentially hold all of my music and photos, plus a few movies.
The 3G version is intriguing, but I don't think I could justify the $130 premium for it, though I do like that you don't have to sign a contract.