This will be a short post, I just want to let people know how much trouble I've had trying to find something definitive that calls out how the Magento Solr integration built-into Magento Enterprise Edition v1.12 does NOT SUPPORT Solr version 4.1 - in fact, I still can't find any "smoking gun" documentation to confirm this, only a handful of reports about various bugs when using 4.1 such as this one regarding "Unknown commit parameter waitFlush" found on Stack Overflow:
It's surprising that there's not clearer (any?) documentation specifying the major revision of Solr to use. It's probably out there, and I suppose someone will rub my nose in it soon, but we've been scouring the Internet and haven't found anything that makes this more obvious.
So, let this be your validation, Solr web searchers: Use Solr 3.6 with Magento for now, not version 4.1 !!!