None yet. I don't like the fact that iPads do not have SD slots and are too 'closed' for what I would want to use it for (though iPads are fantastic if they meet your needs). So I'm waiting (no rush) for an android/linux version with SD, usb host, HDMI at a good price ( ~ $200). Probably a year or two out for me - the ones I see at that price get middling reviews.
If I could put my T-Mobile prepaid Gold Rewards SIM card in it, then I might go for a cellular connection. You can switch to $2-$3/day data connection with unlimited talk/text (Pay-By-The-Day PBTD) for any day/s you need, and then switch back to the 'regular' Pay-As-You-Go (PAYG)for days you would not need data outside of WiFi, or need a lot of talk/text. The PAYG, on Gold Status (put $100 on the first year), takes only $10/year to extend the service - of course limited minutes, but they roll over.
-ERD50