They could ignore any PR juice from the link and not crawl through the link. But they could still use the anchor text to understand what's at the other end. And crawl the page from another url. That kind of ruins the whole original point of nofollow mind you.
I do think they still use the nofollowed link data in some way. We've recently been cleaning up outbound links on our site to 404 pages. Even if Google isn't crawling those links, they still have enough information to know that we link to xxx number of 404 pages, which quite likely doesn't help put us in a good light.