The AWS seminar is definitely worth it. And then the one week class AWS gives right before the test is excellent.
I just went through the whole thing. I tested December 12th, and got my grades back the 27th.
There are three tests involved, and they have to be completed in 2 hours each. The first part is General Knowledge and is 150 questions closed book. (Part A)
The second part is Part B, the practical test. Part B is the compiled welding standard GTAW mentions. This is where most people who miss the test mess up. Part of the reason is the samples are pretty beat up and may confuse people. With the proper preparation it'll go well. Another part is if you have lots of experience in inspecting, it may well work against you. As GTAW mentions, accept or reject based on the supplied criteria only. Some of the porosity is unbelievably huge, but depending on the criteria is acceptable.
Part C is your Code section. I tested with API 1104 and it sounds like you will be also. Both Part B and Part C are open book, so memorization of formulae won't be an issue.
I understand it used to be harder, with much more math. The one week immediately preceeding the tests is invaluable. They really drum it into your head.
There are a lot of welding symbols questions, maybe 16. So know those cold. Lots of questions on welding processed, too.
To pass, you'll need to get 72 on each test.
Go to the AWS site, they have downloadable versions of Part B, and other aids.
Hope this helps, and good luck with your test!