They were indeed gone. I checked at about 8am (EST) and they were not showing up on the right hand side. Now, if you go there, they are now available. But they were down all weekend.
First reports I've seen were on Saturday, with complaints that people wanted to prep for the test and take the test over the weekend.
Google confirmed the issue this morning and a couple hours later the issue was resolved. Google's Bindu said:
Yes, this is a known issue, one we're working to fix, for the time being, I suggest everyone follows Calin's workaround and I promise to update this thread once i have updates :)
By the way, Calin;s workaround was to use the Google Cache.
Anyway, I refreshed the page a minute ago and the exam materials are back. Here is a screen shot:
Forum discussion at Google AdWords Help.