I've run into a rare few sites that have been "hijacked" to display unauthorized messages, and based on these "encounters" I had the impression that the principal use of Scroogle was to search for porn. Google has imposed some "de-emphasis" of suspect hits in their results, so for that purpose perhaps a different engine is needed.
Ads I've seen recently offer to "install links" to make Scroogle available (i.e. be your search engine) for that specific kind of search.
One can Google Scroogle and get some information on the service, but the first few results (at Wiki, for example) are "limited" in the information offered.
It appears that Scroogle simply "passes" your search request to Google, then "scrubs" the ads off before sending Google results back to you, (possibly after adding "paid commercial announcements," disguised as "not advertising" to the listing of results(?)). At the current level of advertising by Google, I don't find it difficult to just ignore it, without needing a "special service" to remove it.
The "visible business plan" is too tenuously defined to rouse my interest, but maybe if Google continues to move toward more and better targeted advertising I might be inclined to investigate further. ... later ... ... or much later.