SEOBook has a very informative article where it answers whether a 301 Redirect counts. Aaron Walls starts by saying the first step is to "find at least one navigational type search query that can be created out of the inbound anchor text of the site you are redirecting, before you start redirecting 301, which you would still expect to rank for even if you had no page content."
"When the new site ranks well for that query you know the search engine is following your 301 redirect, though it might take a bit longer for the trust to propagate through the new website and get your contents fully indexed. As time passes you will see the new site replace the old site for more and more search queries. If it ever stops ranking you know there is a technical error with the redirect (such as accidentally writing over your .htaccess file) or they are no longer trusting or following the redirect.
If you are a large corporation or large Google advertiser then Google will go out of their way to work with you to ensure the redirect counts and the transfer is smooth. Here is an example post Matt Cutts made about helping migrate Microsoft Live Spaces:
Ã¢â‚¬Å“By the way, it looks like the primary issue with the Windows Live Writer blog was the large- scale migration from spaces.msn.com to spaces.live.com about a month ago. We saw so many urls suddenly showing up on spaces.live.com that it triggered a flag in our system which requires more trust in individual urls in order for them to rank (this is despite the crawl guys trying to increase our hostload thresholds and taking similar measures to make the migration go smoothly for Spaces). We cleared that flag, and things look much better now."
The entire article is available at SEOBook.