When I got my first touring bike I was a bit nervous getting bar end shifters having only used STI. After 5min on the road I had pretty much forgotten about them - easy to use and haven't had any safety issues using them. My girl friend and I rode the Great Divide Mountain Bike Route last year using them without any problems; we were quite often on rough steep ground.

I think rogerstg makes a good point about handlebar selection - we both have nitto randoneer bars on our bikes and these spray the drops out a bit (which I really like). I could see that with a more traditional bar there could be some knee problems with the drops closer to the frame depending on bike setup. I occasionally knock one of them when getting on/off the bike but it is very occasional.

I don't know how long bar end shifters are supposed to last - we have both had rear shifting problems whilst on tour; with mine I think it was the shifters but Nancy's was a wearing rear derailleur. In both instances we could use most of the rear cassette except for one cog (so we wouldn't have stuck in the middle of nowhere if we had STI) but that cog was a gear we used a lot for climbing so it was useful to be able to switch to friction mode.