I've been pained by the approach of Google of returning what is subjectively true (i.e. their algorithm estimates relevance), to what is objectively true (i.e. this pattern of text exists, therefore this is relevant).
I appreciate the need to understand PCRE syntax severely limits the audience of such a service, but would you use it? I'm thinking of limiting the crawler around technology and software sites, in particular bug trackers, open code repositories, and mailing lists. This won't be a tool to search for all references to $latestCelebrityScandal, instead think Google Code Search (RIP) on a wider scale.
Google won't allow regex searches because they believe they are not commercially viable (http://www.youtube.com/watch?v=lYiTIDgejas). It's (subjectively) true that the service would cost money to run, so how would you be willing to cover the costs of you using it?