Well I passed the DCD5 exam at the start of the week and I thought I'd share my thoughts on how I found the whole experience.
Firstly I don't think I've revised as much for an exam ever, including at University. In terms of course material like many I found Scott Lowe's design book very useful and even though it's for 4.1 a lot is still relevant especially the design concept stuff. Frank and Duncan's book(s) are a good read as well and as they aren't that long it makes them all the better. I also can't recommend highly enough the vBrownbag podcasts, either seach iTunes or take a look at http://professionalvmware.com/.
I personally found elements of the exam brutal, not least sitting still for four hours!!! and every time I had one of the multi-answer drag questions my heart sank!
You are definitely under pressure in terms of time, it's not even neccesarily about knowing the answer more about the time it takes to read a page full of text and decipher what is actually being asked. With an hour to go I seriously didn't think I'd get through all the questions.
All in all I think that if you are doing design work on a regular basis - not necessarily focussed on vSphere - you'll find elements of the exam easier. Yes you need to know the ins and outs of pretty much every aspect of the product but some questions tend to lean towards general design work.
Oh and know everything off the blueprint, when I came out I looked back through it and pretty much every element was covered in one form or another.
Good luck to everyone taking the exam, I'm off to study up for the DCA exam, haven't decided whether that will be easier or not.