This kb article I found explains the basics. What do you need to do for registering license for a desktop product bought at VMware.
If you don't you might not be able to come back and get updates for your products.
1. Navigate to the VMware Account Management page by going to www.vmware.com/account.
2. Log in with your credentials and click Register a Product.
3. Enter your license key. You can include up to 50 license keys and register them all at the same time.
4. Complete the required fields and click Continue to register your VMware software.
Not only registering your desktop software, you will need to do the same for your vShere 4 license too. If you're a small shop and you bought your vSphere license on line directly, you need to register too to be able to get future versions, like the 4.1 which will will be released in the near future…with new features.. 😎
Source: VMware KB.
I should probably go hear and register my copy that came with VCP last year.