I love my hydropacks... my main backpack is a small rock climbing bag with a 1.5 litre reservoir, I have a Camelback (1.5 litre) which is more compact and my hiking bag and backpack have a 3 litre tank.

Bottles have their place but a hydropack can be very useful on and off the bike.

I don't care what the real roadies think and wear socks and sandals too.