i think the main thing is getting back on when you get back no matter what happened on holiday.
i did it twice last year, lost weight, went away, didnt go back on diet.
the second time i decided to do it, i left it till quite close to going to egypt and was annoyed with myself, as if id have carried on after my first holiday id have felt a lot better.
then when i got back, i didnt carry it on, made a couple of half hearted attempts 'oh i'll wait till ive been out' or 'i'll have this meal then do it' etc, then didnt bother. ive managed to put ALL of what i lost last year back on.
so yeah, my point is...get back on it as soon as you come back no ifs or buts.