This seems related to the new domains recently bought by Google: search-mashups.com, mashsearch.com and other similar domains.
MSN Search (Windows Live Search) already has search macros, that allow you to define a list of sites where you'd like to search (for example, sites about recipes). Rollyo lets you define a list of trusted sources and create your own search engine using results from Yahoo.
So we should expect a similar offering from Google, that will most likely include a way to share your search mashups that combine content from more than one source. Until then you can already do that, albeit not in an elegant way.