Very useful thread underway at the SEroundtable forum about affilaite links and getting credit for them in Google. Basically how do you get the best of both worlds? Pk, one of the moderators is wondering how to get Google to not spider the specific affiliate links multiple times (www.mysite.com/?aff=333) but still give him credit as backlinks. He asks "How the heck do I get Google to give my main site the link juice WITHOUT making duplicate copies??"
Lee Odden, comes in with an great answer:
Solution was to do as you've suggested. Serve Googlebot a non affid url and to 301 redirect any incoming requests that do include the affid to the non affid url. Cookies capture the data to give credit for affiliate sales.
Continued discussion at SEroundtable Forums - Google Indexing Affiliate Strings