It won't warp the neck.
The force of gravity on the neck is much less than the force asserted on the neck by those strings under tension.
I would still not advise long term storage of guitars by hanging them on the wall.
The safest place for your guitar is in its hard shell case.
While hanging on the wall your guitar is far more susceptible to changes in humidity and temperature.
And these changes can definitely have an adverse effect on the wood your guitar is made from.
You can also experience finish issues with some nitrocellulose-based finishes when they're left in contact with rubber and foam, such as you might find covering the guitar hanger's hooks, for any period of time.
It can discolour the finish and even rub it off the guitar with little effort.
And then there's the accident factor: a guitar hanging on the wall is far more likely to be bumped, banged, knocked, touched, dropped, sneezed on, puked over, drooled on, viewed by potential theives...
you get the idea.
It's just not wrapped in the layers of protective foam and plywood that a case provides.
music.stackexchange.com/users/394/Ian C.
I doubt it.
Every single music store I have ever been in hangs instruments from the headstock.
If it caused damage I don't think use of them would be so widespread.
music.stackexchange.com/users/568/Samuel Andrew
It won't except for the effect of weather.
But no matter what you do, don't let it lay flat on a surface without supporting the neck.
music.stackexchange.com/users/None/
It'll do less damage than your kid running into the guitar on its floorstand and knocking it over, then falling on your precious instrument.
music.stackexchange.com/users/None/
I'm doing it for many years now, without any problem... except the kids issue mentioned before of course :-)
music.stackexchange.com/users/None/
I like to leave my guitars out, otherwise I don't play them. I have a couple of wall hangings and stands all over the place too. Will hanging a guitar from the wall damage it at all? Warp the neck? etc.
Will hanging a guitar by its headstock damage it?
music.stackexchange.com
<guitar><storage>
music.stackexchange.com/questions/2638
music.stackexchange.com/users/71/yossarian
S3: The safest place for your guitar is in its hard shell case.  While hanging on the wall your guitar is far more susceptible to changes in humidity and temperature. And then there's the accident factor: a guitar hanging on the wall is far more likely to be bumped, banged, knocked, touched, dropped, sneezed on, puked over, drooled on, viewed by potential theives... Hanging a guitar by the headstock will not warp the neck. While hanging on the wall your guitar is far more susceptible to changes in humidity and temperature. And then there's the accident factor: a guitar hanging on the wall is far more likely to be bumped, banged, knocked. The safest place for your guitar is in its hard shell case.  
Hanging a guitar by the headstock will not warp the neck. While hanging on the wall your guitar is far more susceptible to changes in humidity and temperature. You can also experience finish issues with some nitrocellulose-based finishes when they're left in contact with rubber and foam, such as you might find covering the guitar hanger's hooks, for any period of time. You can also experience finish issues with some nitrocellulose-based finishes when they're left in contact with rubber and foam, such as you might find covering the guitar hanger's hooks, for any period of time. And then there's the accident factor: a guitar hanging on the wall is far more likely to be bumped, banged, knocked The safest place for your guitar is in its hard shell case.  