We had our OWSUG Study group exec BBQ today and the discussion came up on whether or not 70-620 counted as an elective or the core workstation OS on the MSCE. Referencing Trika’s blog, the answer is it counts as an elective or core but not both.
For example, if you were working towards your MSCA, passed 70-270 (XP) already and then wrote 70-620, then it would count as the elective. If you however were starting out and wrote 70-620 (Vista) first but did not write 70-270 (XP) then 70-620 (Vista) would count towards your Core workstation OS. If you did that, then I would recommend you write 70-622 (Enterprise Support) as your elective.