Deadlifts are like Squats in that as long as you're giving a lot of effort, with good form, you almost can't go wrong (my opinion). Going heavy for fewer reps, or lighter for more reps, you're sure to see results. Now if you're wanting specific results, such as maximum power for instance, you'll obviously want to work with heavier weights. I think you need to find what works best for you. For instance, I usually don't like doing more than 12 reps for any set of deadlifts. So If I'm doing three sets, I might do 12, 10, 8, or even 10, 8, 6, or if I'm going for maximum power, I'll load on the weight and do even less reps. And if I'm doing more sets, I adjust the reps accordingly, but like I said, I don't like to go over 12 reps on my working sets.
As of right now I'm doing deadlifts at the end of my back routine (I've done deadlifts at the beginning before, just to let you know), doing three sets of 10, 8, 6. I'm more interested in asthetics rather than pure strength, but deadlifts are just so damned good to not have them in your routine somewhere. They do wonders for my squats, and overall strength for that matter.
Always concentrate on good form and give it all you've got!