I love 5 set matches, play one every tuesday night for practice, but I have never actually played one in a tournament or league competition, nor would I expect to.
It might be fun in league if that was your only match, but our format is really good, too. We have 3 man teams and play 2 dubs and a singles. (it is a 5.0+ league made up of mostly coaches and their best juniors (age has to be >16), so we would struggle to field bigger teams even if we wanted to!
I wouldn't like it much in a tournament, though. We odn't have two weeks to get through a draw so it is pretty rare to not have to play at least two matches in a day, and that's just the singles.
5.0 all courter. Dunlop Bio 400T with cyclone @ 50, Prince CTS Precision 90
"Tennis isn't easy" - Corners