http://www.jmg-galleries.com/blog/2009/01/22/flickr-collection-on-getty-why-im-not-taking-part/
In the case of the Flickr-Getty offer it is an exclusive agreement. There is a limitation on selling images that are similar or sister images for commercial purposes. Use of photographs selected by Getty to sell on your behalf are OK to use for personal or self promotion. How convenient that they also include the acceptability of Photo Sharing in these terms. Per the terms its also OK to sell prints or books as long as they are limited edition and/or signed. Note if a Getty selected image has been previously sold through a prior licensing agreement either individually or through another agency it is then ineligible for submission.
For those that are new to stock photography exclusivity should be approached very carefully. Many old timers recommend avoiding exclusivity like the plague due to the limiting nature of it. Its tough enough to make a buck these days with photography, but signing an exclusive deal is a sure fire way to cut off other income opportunities. What I find most troubling about the Getty agreement it is that they dont permit the sale of your work on your own web site. Granted for some this may be a non-factor as not everyone wants to deal with the headache of licensing their own work directly. I suppose my outlook on this is that if youre serious enough to sell your photography through an agency you should be capable of selling your own work individually and reserve the option to do so.