There was a woman walking the 3-Day last year who kept her WATER bottle there. With a straw. Quite convenient, if you ask me.

I use the gel flask on long rides. I don't water it down -- my body heat is enough to keep it fluid enough to squeeze out. I do try to keep it upside down in my pocket so it's ready to go, and I do make sure it's completely closed, and I try to keep the top clean so my pocket's not a mess.