I use one on rides over 40 miles. Shorter rides if it is really hot. It is good to have, but kinda bulky so I leave it behind for the shorter rides.

I have found a technique for making "Mega Ice Cubes" I put about 6-8 oz water each into ziplock baggies and freeze them over night. Cubes that big take longer to melt (lower surface area to volume ratio). Mine is a HydraPack, not a Camel Back, thought I have had one of those. The giant ice cubes go into the HydraPack easily, though you may want to make them smaller to get them into the CamelBack opening, which is smaller. Freezing a partly filled bladder then topping with water will work, but if water freezes in the valve it may be up to an hour into your ride before you can draw from it. (Been there done that)