tedster - 8:51 am on Sep 6, 2012 (gmt 0)
Yes, they can "index" the URL - but they won't "crawl" its content and insert that content into the search results, or even be able to shard the content data and rank the page based on those factors.
This means that a robots.txt blocked URL is HIGHLY unlikely to get much if any search traffic. In most cases, the URL will not even appear in the index. It takes links for that to happen, and even then the relevance data Google can access is very limited. For this reason alone, ranking for anything except a site: operator query is rare.
That's one reason I like robots.txt for a quick control on query string "sort" parameters and the like. Sorted product URLs are very easily inserted into social media links by well-intentioned fans, The robots.txt file is a down and dirty way to stop crawling from generating a mess of duplicate content as well as messing up the quality of your site's googlebot crawl altogether.