There's already been some chatter in the community regarding vSphere 4.0 Update 2, including a VMware KB article:
While recently downloading a copy of ESX 4.0u1 for testing, I noticed the download URL was the following:
The link will generally take you to landing page to login if you have not ready logged in:
I thought I try to plug-in "2" and see what happens, to my surprise it actually displayed some interesting text:
When you login, it will throw an error that the download group does not exists.
However, if you tried another invalid entry say "ESX40U3", you'll get an error all together such as the following even before logging in:
So does this mean vSphere 4.0 Update 2 about to be released? Your guess is as good as mine, we will just have to wait and see.