There are many facets to this question.
1) How will this affect my energy consumption?
2) How can I best disinfect my laundry?
3) How can I get my laundry to come out clean?
4) How will this affect my washing machine?
1) Energy Consumption - Obviously, hot water is added energy cost. You gotta heat up the water, but how much does it cost? This wonderfully thorough site gives an in-depth breakdown of electricity uses by the temperature of the water you use in your type of washing machine. According to this site, if I have the typical electricity costs, I save 55 cents every time I choose to do cold/cold instead of hot/warm or $215 over the course of the year. Also, see that same site for a discussion of electricity costs of a front loader vs. a top loader.
So, Cold water is cheaper; yeah for cold water.
2) Disinfecting - If you are relying on hot water to kill the bacteria and other harmful buggies in your clothing, think again. Yes, hot water or hot temperatures will kill off bacteria, people even, but not the hot water that comes from your water heater, it's not hot enough. You need it to be boiling before it would reach any kind of efficacy at killing bacteria in your laundry. It might get some of them, but not the majority of them. You have two options, bleach or the sun. Yeah for the sun! Free disinfectant in your backyard, my fellow clothesline hangers. Both, however, can harm clothing. I think everyone knows what a bleach spill will do to your clothing, but the sun if given too much time will do damage too, think of the item you left in the car's back seat window. This site gives you the scientific reasoning for how the sun is a disinfectant and why it is a better option than bleach. So a hot water washing cycle does not kill off all those scary things you are worried about floating in your fibers.
Yeah for cold water, does maybe only slightly worse than hot water at disinfecting laundry.
3) Cleaning Power - Hot water does work better at getting out and breaking up dirt and grime. Hot water doesn't kill anything in your laundry, but it does help release dirt and gunk in your clothing, that gunk that might be encapsulating some of that bacteria you want to get rid of. Why? Because it's hot. Heat is something in school you added to things in your chemistry labs to create reactions, right? It does the same in laundry; it increases the speed and reactions of the molecules of the detergent and dirty laundry dirt and increases the solubility of the dirt you are trying to get rid of. In other words it makes your detergent work better as described here.
Yeah for hot water, the superhero sidekick to laundry detergent.
4) The Washing Machine - What about your workhorse, the washing machine? You know, I would think the items which job is to get things clean should be clean, but they aren't - Every time I have to clean that grimy soap film off my bathtub I am reminded that self cleaning tubs would be nice. The washing machine needs cleaned too. I was told this by the Maytag washing machine repair man that visited me many years ago to fix the broken belt on my washing machine. He made a comment that the move to washing all in cold is giving him more business because the gunk buildup in the inner parts of the machine create chaos. He advised not to go completely cold if I wanted to avoid seeing him again. For the same reason that hot water works at getting gunk off your clothes, it gets the gunk off the inner recesses of your washing machine where your dirty water flows out. Plus if you are using too much detergent (basically if you are using the amount of detergent your brand is telling you to - think, the more they use, the faster they have to buy more) your build up can really cause problems. He only suggested I stick with doing a hot water load with my whites as a reminder, but this site gives some more detailed instructions on cleaning your washer periodically to keep it running well. Which reminds me, there is leafy mold-like crud hanging around the washing machine's top gasket downstairs; need to clean that sucker.
Yeah for hot water keeping the expensive repair man away!
2 votes for cold, 2 for hot-- we have a tie!
So for me, I run hot water every now and then when I know I have a heavily soiled load of laundry (diapers, work clothes) to boost my detergent's cleaning power and to keep my machine running well for longer. Yet the rest of the time I run cold water to avoid the high cost of heating water, and I hang my clothing out to dry because it's a free disinfectant; I would be silly not to take advantage of the sun and its disinfecting qualities when it saves me the cost of the dryer, which costs tons more than this whole hot water issue.