Have enjoyed reading all the comments on the 12 strings. I am currently having one built by Pimentel's in Alb. NM. I discussed this question with the luthier building my 12 string and he agreed that any well made guitar should hold the standard concert tuning, but that the possibility (note: not probability) of the neck warping and other problems does increase due to the extra tension. A lot of variables could enter here: what is the relative humidity where you live? Do you keep your instrument in a case or out? Do you play outdoors a lot? I think sun and humidity could have more effect on a good instrument than string tension Thus some 20 and 30 year old instruments are in mint condition and some are destined for the great kindlin pile in the sky. He recommended for me to lower the pitch and capo as necessary. For lower pitched voices the lower pitch is a benefit. This is one of the really cool things about a 12 string - the options are considerable and some really creative playing can be done.

One more comment about capos - two of my favorite inspirations on the 12 string - Paul Stookey and John Denver - both used capos. I reckon unless and until I can outplay them (not likely) using a capo is okay.