I am developing a social networking website in the facebook/foursquare-ish space. I have gotten such varied feedback on what platform I should develop in. Of course it will be heavily influenced by who I hire, but i was hoping for a little additional feedback from the larger community. Thanks.
It doesn't matter.
StackOverflow was written in ASP .NET MVC and it's awesome.
Twitter was written in Rails and it's super popular.
Facebook was written in PHP and half a billion people use it.
It's not the technology, it's the community. That's the hard part.
Just pick one and go. Your best bet might actually be to find the technology that the most smart people are using while still working for the least amount of money.
Write in assembler if you're comfortable with that. :)
Some questions you should ask yourself:
My best tip is: use what's best for the job at hand according to the above questions. For me, I'd use Ruby on Rails for the project you described. Rails offers all the tools I need for a large project like that.
Please let us know when and what you've decided :)