>> First things first : it depends on what kind of "indexing" you're looking to do — I haven't worked with CouchDB (yet), but I have with MongoDB, and although it's a great (and fast) data store, it has a "basic" style of indexing as SQL databases.  That is, you can do exact-match, some simple regex (usually left-anchored) and then of course all the power of map/reduce (Mongo does map/reduce as well as Couch).
> 
> Out of curiosity, are there libraries to export records from MongoDB into
> Solr?

Not that I'm aware of, though there has been a bit of discussion around people wanting to do that.  My understanding, though, is that a NoSQL-Solr integration is *exactly* what ElasticSearch is designed to replace.

Though Shay Banon is quick to say that ElasticSearch isn't intended to replace a NoSQL data store, many people (including myself) are wondering whether two systems are actually needed in a large number of use cases, especially if the index persists and is clustered.  Food for thought.

MJ