I've done over 120,000 miles on an XJ900 clutch. It can stand a lot of slipping - you use the clutch to fine control speed in traffic - and fast changes in fast riding generate very little wear.
Hard starts and wheelies are the biggest causes of premature wear, as is incorrect cable adjustment with no free play.
To test the clutch, ride up a slight hill at about 50 mph (depending on the bike) and pin the throttle. If the revs rise faster than the bike's speed your clutch is starting to slip.