On the plane I was on, they had wardrobe-like storage in the posh bit that they used. My guitar case has rubber studs on the fat end so that it can be stood upright, this was an advantage.

It would appear that the hand-luggage size restrictions don't apply to guitar cases, though I suspect that anything bigger would need a seat to itself (I know a harp player who does this. I don't know whether he gets the harp's meals as well, though).

Splott Man