The nn/lm scr blog referenced Sitelines blog who conducted tests on Google Scholar and determined that Google Scholar is missing the most recent full year of PubMed records.

Sitelines conclusion: No serious researcher interested in current medical information or practice excellence should rely on Google Scholar for up to date information.

At the time of the test, Sitelines found that Google Scholar failed to retrieve any PubMed content after February-March 2004!

For further information, including the details of Sitelines Google Scholar test:
http://www.workingfaster.com/sitelines/archives/2005_02.html#000282

I highly recommend reading this. As our physicians and students are interested in finding information fast we need to know the limitations of the tools they are using because often they do not know themselves.