I have just discovered that the MySQL 5.0 Beta Certification Exams are available. The Developer Exams are available now, the Administrator Exams are scheduled to be available by the end of January.
The way to get MySQL 5.0 certified has changed a bit compared to the 4.x exams. There are 2 exams for each the Developer and Administrator Certifications. Only if one passes both exams, somebody can title himself either a CMDEV (Certified MySQL Developer) or CMDBA (Certified MySQL Database Administrator). There are no more prerequisites, so the exams can be taken in any order (which was not the case with the 4.x exams where the Core exam was a prerequisite for the Professional exam).
There are also upgrade exams for people who have already passed the 4.x exams. One exam is necessary to upgrade from 4.x Core to 5.0 CMDEV and one exam from 4.x Professional to 5.0 CMADM. Unfortunately, there is no more detailed information about which topics these exams will cover. It also seems that these exams are not yet available as I have logged into my Pearson VUE account and looked up for which exams I could register. I found that only exams 003-001 Certified MySQL Developer Exam Part I and 004-001 Certified MySQL Developer Part II were available, but no upgrade exams. I expect that more information about this is yet to come.
I successfully took both the Core and Professional Exams of MySQL 4.1 and I can truely recommand to get certified to everybody who plans to get good skills about MySQL. I learnt a lot of things that I probably wouldn't have learnt without taking the exams. There are many things which you probably think you don't need them, but when you come to learn about it you'll find out that it makes your work a lot easier.
To get detailed and up-to-date information, take a look at MySQL's certification page at http://www.mysql.com/training/certification/50/. If you plan to take the exams (and also, if you don't, it might be a good choice) I recommand that you get the MySQL 5.0 Certification Study Guide. If you use this book to learn about the relevant topics thoroughly, you have the best chances to pass your exams.