Short domains are better, but even more so when you’re trying to tap in the address with one hand on your mobile device.
Caroline has posted on the DotMobi blog that they’ll be making available single character dotMobi domains very soon (ie. a.mobi, 1.mobi etc.,) in a similar fashion to their city domains applications process ie. via proposals NOT auctions.
It will be interesting to see who gets the domains and what they do with them.