Personally, I've found that as long as I can move the weight up in some fashion, I'm gaining.
Remember it is called "progressive resistance."
That doesn't mean that you have to work in any particular set rep range per se. It does mean that there should be some sort of increase, either in reps or weight.
If you can lift 100lbs. (pick the movement) for 6 reps with good form, and the following week you can lift it for 7 reps with good form, you are stronger!
There was one system used by the old timers. And I mean the very old timers, back in the 1930's and 40's (I read about it in an old MILO Barbell catalogue). They would perfrom a movement in a rep range of 5's or 6's. Then each time they lifted they would add at least one rep to one set. So, it might look like this on week two: 7-6-6.
The next workout would look like this: 7-7-6. They would progress like this until they achieved 10-10-10. Then they would add weight to that particular movement and begin again with 5's or 6's.
I think if the T-Nation writers have proven anything it is this: There are many, many ways to train effectively. You just have to pick one that works for you. And make sure that you change it in some way after a period of time as the body adapts and gains will become much more difficult to achieve.