We today provided some troubleshooting guides for customers who were experiencing any issues when using Activesync 4.0 on their PC.  Essentially in Activesync 4.0 we changed the model to use RNDIS and this 'may' cause issues with some configurations of personal firewalls, parental control and network traffic optimisers.  The guide online gives directives on how to resolve those issues if you are experiencing any: 

http://www.microsoft.com/windowsmobile/help/activesync/default.mspx

Anyone seen any of these issues on their device/PC?  (feel free to post a comment)