I had braces until I was 15, then wore a retainer for about two years. I stopped for a while and my teeth moved around a lot (but I had had a lot of dental surgery while wearing braces because my teeth were so screwed up so if your teeth were never all that out of place they might not move as much), I tried to start wearing the retainer again, but it no longer fit and my dentist said I would need braces again for another 6 months if I wanted straight teeth. Can't be bothered, that was years ago, so my teeth aren't are perfect as they could be.
I have a permanent wire on my bottom teeth, it is generally worn for about 10 years, if it falls off after that time dentists don't usually reattach it, but if it never falls off there is no reason to have it removed.
I worked for an orthodontist for a year while I was an undergrad, I'm frustrated now that I wasn't better about wearing my retainer, it's a shame to waste four years and loads of my parent's money on braces just because I was too vain to wear it in front of my boyfriend!!