Let's consider a scenario where a candidate takes the exam before June 30, 2009 and fails. Now if this candidate wants to go for reexamination on or after June 30, 2009, he/she would have to take the "new" PMP Exam, which would be based on PMBOK Fourth Edition. However, the good news is that the Contact Hours, which were earned to qualify for the first attempt, would still be valid for the "new" Exam. This information has been confirmed by PMI.
The situation is pretty precarious for anybody planning to take the exam from now until June 29, 2009. You need to have your contingency plan ready just in case the "risk event" occurs.
My advice (or proposed strategy) for PMP aspirants would be this:
1. If you have already started your preparation and feel confident, then speed up your preparation and try to take the exam by May 15, 2009. So, just in case you don't clear it, you may still have some time to go for the next attempt before June 30, 2009. If you don't feel confident, then take approach 2 (mentioned below).
2. If you are thinking of starting your preparation now, then I would say, prepare for the "new" PMP Exam, which would be based on PMBOK Fourth Edition, and take the exam on or after June 30, 2009.
I was in the same boat in 2005, when PMBOK Third Edition was introduced. I started my preparation just 6 weeks before the proposed change in the exam. At that time, I took the decision to wait for the new exam to come out and learn from the mistakes of the "early adopters". However, I waited a bit too long and did not take the exam until Nov 2007 :)
Feel free to share your thoughts and opinions on this matter. I'm sure there are better strategies to tackle this situation.
All the best.