Re: Marathons and energy gels
I have tried the safety pins but fumble around a bit when you're running hard trying to rip the things off. I have one pair of "raceready?" shorts that have the little mesh pockets in back prefer that solution.
I too have settled on miles 6, 12, 18, 22 as the perfect times for me, but as people have said, everyone is different.
Once you figure out they settle okay with you, running your long runs with water only will train your body to be more efficient utilizing fat and preserving glycogen. When you use the gels race day, they'll give you even more of a boost-- that's been my experience anyway.
My preference is to do gatorade at the water stops that are not gel ones, and water at 6, 12, 18, 22 with the gels. I've also found that if I jam it down in one big gulp right as I'm coming to the water station it doesn't work so well. Check your pace and about 30 sec to 1 min. before you expect to hit the stop open it up and take the gel in small squeezes, finishing hopefully just before the stop. Water to wash out the mouth and mix with it in your stomach and you're cruising out of there without the risk of not getting some down, leaving a bunch in mouth without water to wash it down, etc.
Again, these are preferences, try them on your runs and see what works for you.