Well, social bookmarking is all about people liking, and linking to you. In the natural scheme of things that's what will happen over time so that's the pattern the search engines expect. If over a very short space of time they spot links from 100 different social networking sites, they might spot it as unnatural, ie you trying to game the system (don't take that as me knocking you - of course you want your site to be sign or you wouldn't have built it) and reduce the relevancy of those links. I believe Google in particular have this kind of witchcraft in their algorithm. MSN on the other hand probably don't.

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Andy Fletcher, not the famous one.