Read through the cam chain library in the tech section.
But in short, at least in my case after 20k miles the chain stretched only .01". Yet the tensioner was ready to fall out. 22mm projection of the plunger.
The gears are pretty hard, they don't wear.
The guides are coated in plastic, yet when replaced don't pull the tensioner all the way in.
The best we've seen with new chain, new guides and new tensioner is 7/16" or 11mm projection. No one here has seen (or is likely to see) a brand new one. So we can't compare. But I think 11mm may be the way it comes from the factory. For those that have to replace it early, it may be worse.
We have mixted new and old parts without much inprovement. This is from memmory so don't shoot me, it's late. Depending on what's replaced of course. Best effect will be seen if you replace the parts that are worn. (any body got a dead horse?)
Like many manufactures, I think zuki set this one up to require maintenance every 5K miles. If you pop the clutch cover with that frequency, you'll catch it time easily. Or if you take it to the stealer, it'll give them a chance to bend you over.
So IMHO, the major flaw is the fact that the tensioner will come apart and cause a piston to eat a couple of valves. If it could do it's thing, and stop before it fell out. Then the bike would tell us when to get in there and fix it without throwing us over the handlebars.
'nough said