martinibuster - 3:39 am on Aug 12, 2010 (gmt 0)
and prevents leaking of link juice
Not really. If you have ten links on a page and one of those links is nofollowed, afaik, the rest of the links will pass PR as if all ten links were passing links. I don't mean to oversimplify, but adding the nofollow won't make it 1/9th of the total PR flowing. It's still 1/10th.
I don't worry about PR leaks, especially for things like hotlinking to images. I don't care about the thousands of hotlinked pages on my sites. I don't nofollow them. I don't nofollow anything. What matters is that the site ranks exceptionally well and that traffic and earnings are consistently rising year over year.
I would worry more about pages that are dead ends, like PDF files that don't link back to the home page, especially if the site has many dead end pages. If that's not an issue then my focus goes back to more content and more links.