I don't think most businesses/websites bother with a mobile friendly format simply because the demand is not there for 90% of the sites. How many times would you use your mobile to access info about tropical fish, lawn seed, fresh fruit, or genealogy? I don't see this changing anytime (read: years) soon, if ever.
Take a look at some of the SIGs here on NamePros that have .mobi's.. 99% are total dreck IMO.
When might "I" be tempted to use a .mobi site? There have been times I might have liked to check my bank balance or check an auction on eBay.. I can see that being useful.
But the key to the success of .mobi is not buying the domain and sitting on it.. it's development. Until the general public is aware of .mobi and can actually make use of it, it will never catch on in total.
Not to mention, there may be millions upon millions who own cell phones, but the percentage who use mobile internet, or even know how to use it, or have access to it, are very small. Anyone have actual figures?
That's just my opinion..