When you are using Windows Azure as part of a member offer such as the MSDN benefit or the Microsoft Partner Network Cloud Essentials program, you are protected from getting charged beyond the credits from your Windows Azure subscription by a spending limit.
If you are prepared to pay for using more resources, you could use a switch on your account page with which you can turn off the spending limit. Unfortunately until a couple of months ago it was not possible to turn that switch back on!
Luckily it's now possible to turn that spending limit switch on! See the short manual below.
From the Windows Azure Management Portal, go to the menu in the upper right corner and select 'View My Bill'.
You arrive at your Account Page.
As you can see in the yellow banner, this subscription has no spending limit. So if you use more resources than available in your subscription, you'll have to pay for that.
By clicking the link in the yellow banner, you can change the spending limit option.
By selecting the upper option and hit the check mark below, you switch on the spending limit as of the start date of the next billing period.
After some processing, you'll return to your Account Page. The yellow banner now reflects the choice you made in the previous dialog.
See also this article: http://msdn.microsoft.com/en-us/library/windowsazure/dn465781.aspx