I bought a couple of .mobi domains during the domain landrush period. The names aren’t too bad and after seeing this travel site for sale on sitepoint it has given me some motivation to do something with them.
I never liked using a mobile phone to browse the internet, but I know it can be useful particularly if you are out and looking for a bar/restaurant. I just checked my .mobi domains and it looks as though they are getting some traffic, which is always a good start.
Google has also released Adsense for mobile phones, so I think this could be something worth looking into, particularly as the market won’t be as competitive as the www.