I have balance issues so ride with a camelbak. I have sometimes ridden with a bottle and no camelbak (but stop to drink) and find I don't get anymore cooler or hotter when I have one on or not!

I am eagerly waiting to get my hands on the Camelbak Racerbak, a 2.1L bladder that sits in an undershirt and your cycle top goes over it. They are really pushing it for TTs but I would love to have one so people can see that back of the shirts and to not get the little napping the straps of the camelbak does.

In regards to buying, not all are created equal and I have heard of some brands bladders leaking etc. I think you get what you pay for. So even if you don't want to pay Camelbak prices consider at least buying the bladder and putting it into anothers bag (if it can fit of course!)