I haven't had any yet, but I figure as soon as all the good letter names are taken, numbers are the next logical step. It's a gamble, yes, but I figure I have a better chance at this than the lottery.
I own 477.mobi and 8564.mobi
477 has gotten a low $xxx offer that i declined
and 8564.mobi spells VLOG, but no offers yet
But I plan to hold on to these for a while and develop my .mobi's