Search engines with regular expressions?
amock: I think this would be really computationally expensive.  You can build indexes of words, but building indexes of arbitrary regular expressions is much harder.  I think Google did a study and found that even increasing the number of results per page was detrimental to their traffic because the pages took longer to load.  If they allowed regex searches their page load times would increase by much more.However, I would also like a search engine like this.  I don't know how to make it profitable but I think it would be very useful.