A little bit. I've used it with the basic Whoosh. Works fast for single machine installations. Really needs a queue for adding lots of records records, or scheduled re-indexing, with auto-indexing bypass. My older installation is grumpy with threads but newer version should be better..
Can't say I've used it that recently but I know the Whoosh/Haystack combo is being actively used in some smallish government and other Django sites.
Bit of brain picking here. Anybody have experience with haystack?