If your guitar has any of these issues it has sustained damage from dryness. On a positive note most of these issues can be fixed by super humidifying your guitar as shown in our answer to "Buzzing and rattling strings." Buzzing or rattling on one or several strings especially near the sound hole. Getting the same note when fretting certain chords. A leaning saddle (from a bridge tray that dried out and expanded)  A peeling pick guard from the woods condensing which will loosen the adhesive. Loose wires on electrics from the adhesive  drying out that holds the wires down. Looseness around electronic system from dry woods shrinking around it. A cracked bridge or separation of the bridge from the face. Sharpness of frets when sliding your hand down the side of the neck. A hump in the fretboard that sinks down into the sound hole. Flatness or sinking of the face (a guitar's face should bow outwards)  Flatness or sinking of the back (a guitar's back should bow outwards)  Creaking in certain parts of the body. A crack on the face right next to the fret board.  A crack running from bridge to the bottom of the face.  Cracks around the screws of the electronics on electric models.  A crack on the back, neck or heel.