I think anything above 6 - 8 Characters makes no sense under .mobi.
Further, I would say it makes no sense at all to register names that are not directly related with cellular phones. Imho 95 % of all registered .mobi domains will not sold be at the time of expiry in two years.
I've seen plenty of useless TLD's, but .mobi beats them all. Should .mobi be a success, it will only be due to the great names and capital behind it. Actually even they have proven they can make mistakes, and I would say this is one of them.
Sorry, if that is not what you want to hear, but it is my honest opinion.