In preparing for this exam, pay close attention to the exam objectives, as they are subject to change without notice. Remember that this exam is a composite of the material included in exams 70-640 and 70-642. Recently, Microsoft quietly extended these two exams to include content related to Windows Server 2008 R2. Microsoft has hinted that 70-648 will also be updated to include Windows Server 2008 R2-related content.
I also recommend avoiding the brain dump sites. Exams are composed of questions drawn from a pool of potential questions. Therefore, no one candidate sees every possible question. Brain dump sites tend to omit a lot of questions and can be notoriously inaccurate. There are also rumors that Microsoft has set up fake brain dump sites in an effort to catch exam cheats. Therefore, if you choose to ignore my advice and use a brain dump site any way, then you should avoid any brain dump sites that require you to register.