On my old blog relentlus.wordpress.com (notice it is banned) I posted how to mask an affiliate link using ASP.NET. That was one of my most popular posts. I just searched Google for the live example I put up on one of my throw away domains:

http://www.google.com/search?hl=en&rls=com.microsoft%3Aen-us%3AIE-SearchBox&rlz=1I7GGIH&q=how+to+mask+affiliate+link+in+asp.net+site%3Aeverwon.com

Now look at the SERP. First click the regular link in the SERP and look at the page. You will notice it says "Real Affiliate Link" since you are a human visitor. Now click the Cached link for the result. I pasted it here too:

http://209.85.165.104/search?q=cache:btkgTXWsU40J:everwon.com/+how+to+mask+affiliate+link+in+asp.net+site:everwon.com&hl=en&ct=clnk&cd=1&gl=us

Looking at the cache you can see how Google see's the page. It see's "Cloaked Affilate Link", confirming that I indeed cloaked the link and hid it from Googlebot. I'll see if I can dig up my code sample again and get it posted here.

Affiliate Marketing .net