Other applications' exams will follow, as well as the Expert level exams. I will reach for the Excel Expert certification and I'm looking forward for the rest of the exams to be released - just in case I'll go after the Master certification. Will keep you posted on my progress :)
A slightly funny detail of the MOS certifications is that Excel 2007 Expert and Word 2007 Expert exams seem to be still in development, and they are not required for the Microsoft Office 2007 Master Certification. I wonder what's the real status of these?
They managed to release a new full Office version meanwhile but these exams for previous version are not done yet :)
Are you planning on taking the MOS certification(s)? Are you going for the fresh 2010 version or for the 2007?