buckworks - 8:36 am on Sep 23, 2010 (gmt 0)
As long as these footer links from client sites are sending me business
Ummm .... what matters here is that the clients get the maximum business performance from their sites!
Suggestion: Give yourself a few words of credit on the About Us page, where it would be relevant, but not plastered all over the site. If you really want to take the ethical high road, use an unlinked URL.
A new prospect who is smart enough to be the kind of client you'd want would have little trouble finding you from that, and it would totally avoid any questions of interfering with the client site's ability to rank.