As, the latest Google Search Appliance (GSA 6.8) now has faceted search, amongst other things.
We blogged on the GSA last year, noting how – although the GSA has some powerful features – its administrative interface and feed control were both somewhat lacking. It seems that the main new features are: faceted navigation, a SharePoint 2010 connector (useful for intranets), and Active-Active mirroring. How many of the glitches we found back in 2009 (such as poor ampersand handling, batch import control and index purging) are now fixed is not clear, although a side-effect of the new faceted navigation seems to be that the search result estimates are now accurate.
For document-centric searches, GSA is still probably a good bet, but for more complex requirements, something like Endeca or FAST might be more appropriate.