I've seen examples online, and I've messed around with it a little. They have a Zildjian Sprial Stacker on display at my local music store, too, and it sounds pretty cool. While I kinda like the sound I get, for the stuff we play most of the time, there isn't a whole lot of application for it. The other challenge I faced is that they wouldn't project very much, so I'd have to really whack them to get them to the volume the rest of the kit is at, at mediums levels. And of course, it becomes just another thing to set up and tear down, in the limited time that I have, so unless I really like/use something, I can't justify it.
Probably if I had a regular kit set up at home, all the time, I'd probably mess around with stuff like this more often.