Do you find social networking tools effective for reaching executive decision makers?

Now that all sales and marketing executives have a wide variety of networking tools available, it is time to analyze them to understand whether or not they are appropriate for enterprise software sales.  There are obvious solutions like Spoke and Jigsaw that provide contact details in return for a fee or fewer leads in return for sharing your own details.  Unfortunately, the information published on these sites is often out of date, and this is even more the case when dealing with c-level contact details.  More restricted sites such as LinkedIn require a higher level of permission to contact people in the network.  The question is whether or not it is acceptable to leverage the network for lead generation.  On the one hand, it is a great way to access people who are otherwise difficult to access.  On the other hand, it will ruffle a few feathers in the network.  I think that LinkedIn and the other networkng tools need to be treated with the same amount of professionalism required with all referrals.