As a Beta Exam Test Taker, I really cannot say much about the content or format of the tests. I just took my third beta exam (70-443). I felt more comfortable in this exam thatn the other two that I took, but it took me a lot longer. Time just flew by.....
Difficulty - I would have to say that the exams bump it up a notch or two from the older style of exams. There is a lot more "deep" thinking and consideration on each question.
Test Guides - There is a test guide on the microsoft site to give a thumbnail of what is covered. I really can't comment on it more than that.
Want to get involved (and you have studied /used SQl Server 2005)???? Visit the PASS website at www.sqlpass.org to find out more. I just found out that more seats were added to 70-443 and 70-444 exams. You need to act quick as I think the test taking window closes very soon. PASS will also feature soon a web presentation on the new certification tracks for SQL Server 2005. Stay tuned!