The * greekhand referred earlier to in Cutt’s Blog states “Nofollow links definitely don’t pass PageRank. Over the years, I’ve seen a few corner cases where a nofollow link did pass anchortext, normally due to bugs in indexing that we then fixed. The essential thing you need to know is that nofollow links don’t help sites rank higher in Google’s search results.”
The summary theme of his entire blog article on the nofollow is that we should not use it internally within our sites. However, given that it doesn’t pass PR or anchor text, it is still appropriate to use for affiliate links.