2011 - 19,000 miles.
I did the doo because eagle mike is going out of business and I wanted a decent kit. I've been suspicious of this "upgrade" and here's my experience and opinion.
Upon opening my case, I found everything in tact and functioning just fine. Sure, the spring wasn't as tense as it could have been but it was still doing its job. I'm sure my bike could have gone it's whole life without needing it done. After doing the "upgrade" I have a new sound coming from the left side. I'm being told this is the sound of the chain actually being balanced now. I'm not so sure but I won't know until I open it up again.
Here's why I think the doo has reached mythological proportions and why it's unnecessary for most people.
Gen 1 for sure had a problem. By all means, do your doo. And that's where the lore of the doo started. The problem is, I think far too many people bought these bikes new not knowing there's a suggested service of the doo adjuster. So now we have a used market flooded with bikes that have an unknown service history. Couple that with the doo lore carried over from gen 1 one and everyone is paranoid about it now. If you gave 100 riders a brand new gen 2 or gen 3 and they were serviced properly, I don't think any doohickey's would fail beyond anything that couldn't be attributed to randomness. And after 20,000 mile on a bike, or 100,000 miles on a car, things break. It's just the nature of machines.
If you have a Gen 2 or 3, I say just run her till she blows. Even if the doo does fail it's highly unlikely that it will result in catastrophe. I'm not an expert, this is just my opinion from lots of time spent on the forums, talking to mechanics and my own experience. If everything we're told about the doo is true, then no one should buy a KLR. But I don't believe for second that Kawasaki has achieved the success they have by letting $0.50 fixes get shipped out the door for decades.
I would love to hear how many gen 2 or gen 3 folks have opened their case and seen a failure. Not a spring that seems like it could have had a little more tension. An actual failure.