that was my first idea of what to do with it. problem is, i just can't see a vertical engine adding much value to what is already available via the horizontal engines. to work a vertical engine would have to leverage it's knowledge of it's particular area of expertise to produce results that are better than google. other than a few niches i can't see how that would work well.
I can however see SEOs jumping on this for performing competitive analysis. want to know an accurate backlink count for sites linking to another site? well, that would be fairly painless and cheap with this tool.