So, I already wrote that the question of Virtual vs. Meta is not the right question - they are complimentary solutions. One more thought on identifying where each would fit.
Every organization embarking on an IdM journey needs to begin by identifying data stores and collecting, cleansing, transforming & reconciling data. At this stage, traditional synch tools (metadirectory) are probably the right tool for the job.
If you already have a reasonably good set of data and are looking to provide additional or customized views into that data (via LDAP, SOAP, etc.), then Virtual Directory is probably the answer.
Of course, this is a very generalized view, but I think a good starting point. One of the things that make this question confusing is the functional overlap between the two solutions -- and there is plenty. But the point is to find the best fit solution for a given set of business challenges.