I don't think there's much of a risk to email. Email has a few giant advantages that social networks just can't compete with:
1. Nobody owns it. MySpace, Facebook are all at whim of their owners. They can be snooped, modified, crippled, disabled, limited, etc. 2. Email is secure. Email can be done 100% internal (Exchange) or external. 3. Email is manageable. It can be sent to many devices, filters, storage mechanisms. MySpace, Facebook, etc. are all 100% web based, and the org (or individual has no control). 4. Email is universal. This STILL isn't the case with IM. You still can't IM across networks. Social networks have the same thing. No 1 will become dominant. Hasn't happened for search after all those years, not for IM, ISP, or anything else they predicted will have 1 winner.