I recently completed my MCPD by upgrading my MCSD.Net using exams 70-553 and 70-554. I used the notes on this blog and practices tests such as Transcender to prepare. I also spent some time in Barnes and noble looking at the Official Microsoft Training Kit for the individual exams that make up part of what each upgrade exam covers.
So take exam 70-553 for example. Passing it give you the MCTS windows and MCTS web credentials. Normally it would take 3 separate exams to attain those credentials: 70-526 which covers Windows Development, 70-528 which covers Web Development and 70-536 which covers Development Fundamentals. These topics map directly to the 3 sections that exam 70-553 covers. And Exam 70-554 maps to the topics covered in exams 70-529 (Distributed Development) and 70-549 (Design, SDLC etc).
The implications of this of course are that you can use materials designed for the individual exams to help you prepare for the upgrade exams. There is a lot more material available, and right now there is not much besides this blog to help you prepare for the upgrade exams. Especially if you know you may be weak in one area, it might be worth getting one of the training guides for a section you aren't as strong in.
You may have noticed new links in the navigation pain under MCPD/MCTS Certifiction resources for Exams 70-526, 70-528, 70-529 and 70-536. Another thing I realized is that my notes are helpful not only for the upgrade exams but also for the individual exams. So I went back and recategorized all of my notes to indicate which exams they would be helpful for.
I will try to post the links to the Training Kit books for the individual exams later today.