> I know this wasn't your example originally, but it does exemplify a common problem: There is nothing special about sorting restaurant recommendations vs. sorting some other such thing. If you have an unpatentable algorithm which is good at sorting lists of anything it shouldn't become patentable just because you claim it as "sorting restaurant recommendations." Mixing an unpatentable algorithm with a totally obvious application of it shouldn't get you a patent.

Totally correct. The first requirement to patent something it that it should not be a trivial invention (something that is so easily derived from something else). But most patents are, however, trivial in the software world. That is a big issue.