According to Mike Schackwitz via the Inside Windows Live Blog, the roll out of the new Wave 4 version of Hotmail is complete:

Here at Hotmail, we’ve had quite a busy week! All of our customers are now upgraded. The majority of you got the new Hotmail just this past week, as we completed the rollout to over 350 million people in more than 220 countries around the world. Now, everyone can take advantage of a faster Hotmail experience with great new features like one-click filters, Sweep, Active Views and more.

This upgrade began back in mid-June and was initially carried out in a very methodical manner – doing the upgrades cluster by cluster – to make sure no catastrophic issues were hit for users.

According to Mike’s blog posting from yesterday the majority of the upgrades to user accounts have occurred in the last week or so.

If you are experiencing issues with the update and need some assistance Mike recommends you visit the Hotmail Support Forums and provide them the info on your problem.  This forum is being monitored by Hotmail support folks so they should be able to assist.

According to comments on two threads here at (The New Rollout Continues and Windows Live Hotmail Changes Coming) quite a few folks are experiencing issues in reading the source of any emails in Hotmail Wave 4.

I did a quick search in the support forums are there are others experiencing this as well but I do not see a current solution.  I recommend everyone document the error they are getting at the forum so that data is available to the support team and will help them focus their efforts.

On a side note – the ability to read the email source is in a different location in the new upgrade to Hotmail.  Previously you could right click on an email and select View Source.

In order to see the message source now you must click on the Actions menu in the preview pane header for the email and you will find the link there for View message source: