How long do your sails last ??

my concern now is modern sails
people are telling me your most used sails need replacement every 3 to 4 years
on the islands near the tropics i hear they replace them EVERY year
(they often stay rigged all day, etc)

my "modern" sail has seen about 2 full summer seasons and about 40 outings
the monofilm is starting to look grey and the creases sad
the stitching looks bad on one batten to sleeve joint
some people say ride it to the end with some repairs as needed - others say replace it

what say you ??