I've been using the plugins "relevanssi" and "dave's live search" and they work well together, but have noticed a bit of a lag and slowness sometimes (especially when waiting for the "live search" to pop in. My site http://www.membershipexpert.com isn't too large, a few hundreds articles and not a lot of videos or audios yet, just plain text, but you can tell the Wordpress search is struggling a bit under the load. I don't blame any one plugin but when you're running many plugins (30 or more), sites can slow significantly under the strain. Offloading the search seems like a great idea and is one less thing to tax your server.