I have it on all the time. Except when fighting, that's the only time it's off.

I have it on all the time. I call it Splinter Cell mode.

I hate having it on as I really hate the way it looks, but since I'm trying to get the Perfect Knight trophy I only take it off during combat. I don't want to miss a thing.

I only use it when I'm lost, or when in a stealth section. Though I often forget to turn it off until I start beating up on x-rayed skeletons.

I hate having it on. but i use it quite a bit. I dont use it in fights though.

At least half the time, it would have been better if they integrated it into your view without it changing the entire look of the game.

Almost always on, since I often forget to turn it off in fights.
 
I hate it, cause it's a waste of beautiful graphics, but not as much as I hated the similar view in "X-Men Origins: Wolverine". That really was a pain in your eyes.

I was in the mode a lot, always looking to see if I could find a riddle, or a wall that could be blasted down (for an easy trophy). Sometimes I forget to turn it off when I'm fighting. Doesn't really matter that much, though.

Nearly all the time, I'll turn it off a lot so I can enjoy the environment though.

Over half the time.  It's too important.  Otherwise you miss things like Riddler maps or other pickups, you miss walls you can blast too much...  It's a shame it takes away from the visual quality and atmosphere.  Would have been better if it was an effect that added to it, like the flashlight in Shadow Complex.

It is on most of the time, actually. I intentionally turn it off to enjoy the graphics and fights but when I am running around and, of course, detecting stuff, it is on. It also looks awesome.

70% of the time

a lot!

I just use it to scope out the place, then stealth up to the fools a choke them out

Roughly 40% of the time.

60% of the time.

On medium, almost only in predator rooms. But when I went for the riddles I had it on quite alot. On hard however, I had it on like 80% of the time.

I used it mostly to see if the lunatics were in the area because I hated getting ambushed, and it made a lot of vents a lot easier to spot.

a lot

60 - 70% of the time. The X-Ray vision helps but the lack of colors made it hard for me to navigate properly a bit during my first playthrough. It's also pretty difficult to observe enemies through multiple levels of a room so I have to occasionally turn it off just to be sure I'm looking at a bad guy instead of an empty floor. In fact, I'm pretty much turning it on and off most of the time and the sudden white flash it does is actually starting to annoy me now. Good thing I'm not an epileptic or else I would've been hospitalized the first day I played this game.
 
I honestly don't have a problem with detective vision except that stupid white flash every time I change views.

Almost half of that game I was in DMode.

I'd say around 30%.

I remember being over 60% of the game in detective mode, don't know why though. =]

My first playthough I had it on around 40% of the time. Used it very frequently, but in subsequent playthroughs where I already know where all the riddles and such are I only turn it on when I really need it which is mainly on predator sections.
 
In all honesty, you really miss a lot when you have it off as far as the visual mood and ambiance of the game. I had it on so much on my first playthrough that I was a good bit through the later part before I realized it had all gone pinky/red. :P It really helps the atmosphere to turn it off. Trust me.

i only have it off when im in combat or there is some impressive scenery

Almost constantly.  Again, I turned it off during combat or when I got to a new area and wanted to see some of the scenary..  But for the majority of the time it needs to be on.  Either to see where enemies are, finding your way to the next objective or solving the Riddler puzzles.  And say it was one of the only bad points about the game, I do like the idea, but the fact it needs to be on 90% of the time kind of ruins things.
 
Hopefully it can be streamlined for the sequel.

I have it on all the time now looking for all those damn riddler trophys

I try to have it on as little as possible.

I use always use it except for when I'm in combat. I'm honestly surprised that it didn't have some kind of battery/energy meter for it that seems to be all the rage for ultra-useful accessorizes these days.