Good timing - just this week I read a clarification about this topic from a Googler. What I read was that as long as such a link goes to the site that provided the service, then it's fine. What Google does consider a link manipulation is something like a "sponsored" Wordpress theme - where the link(s) involved are sold to various different sponsors or advertisers.
I'm going to look fo that reference now - wish I had bookmarked it :(
[edited by: tedster at 7:57 pm (utc) on Feb. 24, 2008]