I've only been in one house (mansion) that had lowV switches controlling 120V lights. It was an old, but well installed system, and had a neat doorbell/pager with numbers that dropped down according to which door was ringing. It was all a bunch of relays, contactors, and lowV wire strung everywhere, but no voltages were mixed except in the control wiring box. I made some routine repairs and it still works great!
I haven't had the opportunity to deal with anything modern. The Greenbrier houses have releatively normal wiring, with VDV/Audio guys doing their thing. What they do is some pretty fancy stuff! ...Invisible speakers in the ceiling (better make good connections the first time!), huge HDTV sets, sound system controls in every room (that sounds like crap, my computer has much better bass response on a $60 sound system!), intrusion alarms system and intercom...
None of it is my resposibility, thank goodness!
