There are a number of companies that are running vSphere4 with the Nexus, I am moveing this question to the vSphere forums for a greater audience
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Tom Howarth VCP / vExpert
VMware Communities User Moderator
Blog: www.planetvm.net
Contributing author on "[VMware vSphere and Virtual Infrastructure Security: Securing ESX and the Virtual Environment|http://www.amazon.co.uk/VMware-VSphere-Virtual-Infrastructure-Security/dp/0137158009/ref=sr_1_1?ie=UTF8&s=books&qid=1256146240&sr=1-1]”.
FYI: I bumped a similar forum question on the 1000V and got resonse over here.
Cheers!
Sean Clark
@vSeanClark