A large number of Web 2.0 companies aren’t making any money, or at least no revenue, despite being popular, according to entrepreneurs and financiers in the know.

Many sites offering social networking, providing space for user-generated content, and offering other cool online services, just aren’t successful when it comes to bringing in the cash. Some observers are predicting that the myriad of startup companies currently trying to get noticed will be gone in the next couple of years, leaving just a handful of financial successes…