How much is "LOUD" still a reference point for some?

The magic is in the first watt.

Never really given this any thought. I remember as a young student seeing Van Halen in Concert at NC State and could not hear correctly for the next 2 days. I told myself never again. I enjoy my Maggies at 70-80 Db depending on the music being played. Its nice to physically feel the music and still hear all the detail. For me 90-105 is loud and at this level my brain fails to process detail well, hardly the speakers fault. 

I like to listen loud after a few beers, so not a lot.  I measured 105-108 on the scale.  I would like it louder, but that's about as loud as it goes.  It's still clean at that volume.  NAD and Performa speakers.

With live-recorded acoustic music, an excellent audio system should be able to fool the blinded listener into believing the musician is in the room with them. 

Amplified music like rock concerts present a lot of sonic variables depending on listening position, but a great audio system should be able to replicate what the front of house sound mixers can hear at the ideal position of their mixing boards...center spot about as far from the stage as the stage is wide.

Headphones won't work, because we need our skin to feel the vibrations of the music for it to be like being there at the time of the recording.  High efficiency speakers with low distortion and stereo bass reinforcement powered by amplifiers with generous power reserves seems like a minimum requirement.

Studio albums are wholly different because they usually aren't trying to capture a "live" sound.  They are making a piece of sonic art whose characteristics are subject to the whim of the artist and recording engineers.  But sometimes they still sound great loud.

It's nice to be able to play realistically at concert levels, even when you prefer not to.
 

The ability to play loud is essential for me.  It's not so much that I listen at crazy levels as I appreciate dynamics.  The cannon in the 1812 Overture should sound (and feel) like cannon.  I use my speakers to earn a living mixing music and film, but I also use my studio as a listening room and (in the old days) gatherings and listening parties.  I want to hear the quiet parts quiet and the loud parts loud. And even though all my fan-equipped gear lives in isolation racks there is still some low level residual noise perceptible in the room.  My JBL M2s can play quieter than the noise floor and resolve accurately down to where I can't hear them anymore.  Loud is essential.  Quiet is essential.  Those two qualities give perspective to everything in the middle.