There was a thread on this a little while ago. Run a search first.
I've worn custom orthotics since I was in eighth grade. If I hadn't, I probably would've gotten a lot more injuries than I did, not to mention your average aches and pains, so having them is much better than the alternative if you really need them. Why are you getting them? Who said they were a good idea?
The only time needing orthotics or having flat feet becomes a problem is if you have rigid flat feet, which is more rare. Look up flat feet on wikipedia; it'll tell you what you need to know (at least in this instance).