Barry Schwartz has written a post on Google officially requests webmasters to block internal or external search results. Barry informs about a Matt Cutts post namely Search results in search results which revolves around a query raised on Google's Webmaster Help Group.
Philip Lessen inquires:
Is there any official Google statement regarding that search result on one's own site ought to be disallowed from indexing (e.g. via robots.txt)? It's a trick many spammers use, after all, and sometimes, it happens inadvertently. And it creates a lot of redundancy in search results.
His query was followed by an example of YouTube search results in Google Web search results.
Vanessa Fox replies to the post:
Typically, web search results don't add value to users, and since our core goal is to provide the best search results possible, we generally exclude search results from our web search index. (Not all URLs that contains things like "/results" or "/search" are search results, of course.)
Google does not want to show their own properties search results in the Google search results. Nor do they want your search results to come up, if they don't add value. So I suspect, I should disallow searchinternal.html from this site to show up, because at least one result has been indexed.
For a better insight read the complete post.