Having installed VSphere4 on my laptop, cramming the white papers consistently for two months and attending the 'What's New' Course I thankfully passed the VSphere4 exam at the first attempt and hence upgraded my VCP3 status to VCP4. With the relief of passing the exam, I felt it might be useful to pass on some tips and advice to fellow virtual addicts who may be thinking of attaining the certification.
Firstly and most obviously you have to maintain your hands on experience, not just with VSphere4 but also ESX 3.5. I was surprised at actually how little has changed between ESX 3.5 and VSphere4 and it is easy to get caught up with the notion that this exam is only going to focus on the new features of VSphere4 leaving you to possibly neglect reminding yourself of the core skills and concepts you use on your ESX 3.5. While you definitely need to know about the new features such as Data Recovery, the Distributed Vswitch, VApps, Thin provisioning etc. the exam will still pull out some tricky questions related to core stuff such as HA, VMotion and VStorage.
So my tips in preparing for this certification is to firstly give yourself at least 2 - 3 months hands on time with VSphere4 even if you are well versed with ESX 3.5. There are many ways to stick VSphere4 on your laptop (just google ESX on a USB stick and you get some great results) and the Distributed VSwitch is also available on a 60 day trial basis as well as other features.
Secondly I think it's essential to go on one of the courses, although I must admit that the two day 'What's New' course did pack a lot in and could easily be extended to a 3 day session. The course material and labs offer you the chance to link mode datacenters, migrate virtual switches, use DPM on hosts etc something a bit tricky to achieve if you have limited facilities at your work site. I always find you learn more by making mistakes and troubleshooting - something which you can afford to do during the course labs on the course.
Thirdly as well as the course material and configuration manuals, you must download all the white papers and go through them. You will inevitably face questions that refer to information specificaly mentioned in the white papers and no where else, but the good news is that all of these are easily available for download from the VMware site. In addition to this a great book to use and one which will guide you through and also remain as a sound reference is Scott Lowe's Mastering VMware VSphere4 book.
Lastly and what I found to be the most useful of all resources are the blogs and sites of Simon Long and Scott Vessey. There you will find direct links to just about every document you need as well as great tips on how to get the best out of your VSphere4 platform.
In conclusion I preferred the VSphere4 exam to the previous VCP3 exam for several reasons - very few questions if any on silly memory games such as configuration maximums and more questions focused on knowledge of what you actually use and access on a daily basis in your virtual environments. My only gripe is that it's still a multiple choice exam and being a techy freak I long for the day when VMware will go the route of RedHat and offer a fully lab intensive exam - but then again that is probably why they also offer the VXDX!