From [google.com...] [edited by: Marval at 9:52 am (utc) on July 17, 2007]
The pther place that you would be wise to use them would be advertising partner links as discussed in the new Google WM Guidelines:
"Not all paid links violate our guidelines. Buying and selling links is a normal part of the economy of the web when done for advertising purposes, and not for manipulation of search results. Links purchased for advertising should be designated as such. This can be done in several ways, such as:
Adding a rel="nofollow" attribute to the <a> tag"
[edited by: Marval at 9:52 am (utc) on July 17, 2007]