I use Streamlight for normal "duty" flashlights and have seen all kinds of stuff go wrong with them, but that is also counting lots and lots of heavy-duty patrol grunt type abuse. They fix up easily and continue to keep chugging along. Every car has an Sl-20 or two mounted, and everyone also gets a stinger issued as a "back-up." I also have an issued Scorpion, which tends to be my favorite. I had a really nice SL-20X (the lightweight plastic full size), but I finally managed to break it, after driving off from a scene for about the 10th time with it still on the hood of my patrol car; it still lit up, but the tube was broken. Streamlights are great for constant use because of the fact that they can mostl be recharged.
I use Surefires for weapon lights. They also tend to have problems, especially with the pressure sitches. Most of the Surefires we use are around 10 years old, though. The reason for that, and the reason we haven't replaced any of them, is because Surefire will continue to repair them, forever. They have excellent service, and out standard turn around time is about a week and a half. Heck, they even completely replaced a forend light for me a while back.
The newer Surefire weapon lights seem to be much more expensive, but much more of a "mature" technology. We are buying some this year, if they don't cut my budget anymore, but I am having a hard time convincing my boss; the really old lights we have work just fine, and Surefire keeps fixing them. I don't doubt that some of the lights we are using now will still be around in 15 years when I retire.