OSC principal Eric Pugh took part in developing the Solr certification test with Lucid Imagination. You can read his thoughts on the value of the Solr certification exam.
"I expect that the Lucid Imagination certification will quickly become the gold standard benchmark for whether someone who claims Solr and Lucene expertise truly possesses it. Oftentimes, a buyer of services has to take the leap of faith from sales pitch to execution that the knowledge is truly there. This certification can show, without a doubt, that the holder truly has the knowledge required to deliver a successful Lucene/Solr implementation. -From Reuters, Eric Pugh