I use the following system:
Delicates are always separate (but single guys typically don't have to worry about that).
Whites by themselves, hot water wash w/ bleach (that's the only way they'll stay bright)
- note: screen printed white T shirts and white socks w/ grey inserts can typically be safely bleached
Light colors together, warm water, no bleach
Dark colors (incl. black) together, cold water no bleach
3 - 5 oz. plain white vinegar with the (always cold) rinse as a softener (works especially well at neutralizing bleach w/ white loads). The vinegar is also very good at killing odors of all types.
Towels, washcloths, socks, underwear, gym clothes and sheets are ALWAYS warm or hot water. Be especially careful of colors, though, when you're dealing with towels. Light colored towels can REALLY soak up dyes and get discolored when washed with dark clothing.
When drying, clothing ALWAYS gets low heat, except whites. Some clothes shrink, some don't, but nearly every clothing label says "low heat", so why take a chance? Some delicates, including sweaters, need to be line dried or laid flat. Stuff that's not clothing or any white clothes (since they're washed hot) gets high heat. High heat dries better, faster and, if you believe the manufacturer of my dryer, is more efficient.
Regarding water temp, I was washing nearly everything cold for a while, but it just doesn't come as clean that way. I was getting moldy smells from freshly washed bath towels, for instance, and my gym clothes NEVER came clean and always smelled bad. You NEED warm and/or hot water whenever you have something potentially smelly, sweaty or moldy. Hot is essential to keep your whites looking sharp.