I just flew Delta to and from Folk Alliance/vacation in Florida. I saw guitars as carry on during both flights and no one took away my water in either LAX or JAX. I think the trick to flying with instruments is to follow the "rules" that I have seen published elsewhere: (1) get a seat at the rear of the cabin so that you can board first and there will be room for your instrument in the overhead compartment. (2) be nice to the security personnel - they don't get paid much and they get blamed for everything. (3) call the airline and let them know that you have an instrument and ask for their assistance and suggestions (different airlines have different rules).

PS - Nicole, Delta told me that security taking bottled water was an urban legend. It is too weird to hear that it actually happened to you. thanks, Amy