A couple of comments on my experience. Like some of you, I purchased the PMDD Premix before really knowing what I was getting myself into. And as a result, I have 4 lbs of Premix that I need to use somehow or just throw away.
I have a 46G bowfront tank with 192 watts of CF lighting, pH controlled CO2 injection. Having read somewhere (don't recall where any more, probably Estimative Index) that you can use nitrate as a marker for the major nutrients, I decided to try dosing the Premix to get my nitrate up to approx. 10 ppm with each major water change (change 50% of the water each week). Our tap water here seems to contain around 5 ppm nitrate so I knew that I was going to get a bit of excess but wasn't particularly worried about it. I dumped 2 tsp of the Premix into a small Minute Maid plastic bottle, added half of the bottle's volume in water, and shook vigorously to get the powder to mix well, and then dumped into the tank. I went like this for about 2-3 wks - decent growth on my stem plants (in particular, the Elodea) but nothing to write home about. Some BBA started to appear on my slower growing plants and on the gravel. After the realization that PMDD Premix doesn't contain phosphate and that my bioload while on the higher side wasn't supplying enough phosphate for the tank (phosphate level would drop to 0 right before the water change), I decided to supplement with phosphate in addition to the Premix. After buying some potassium phosphate from Greg, I created a concentrate such that 2 cc would add 1 ppm to my tank and placed this in a medicine bottle with a syringe draw port attached so I could measure out the liquid precisely.
After having added the phosphate in addition to my usual Premix addition after a water change, I went away for a week and came back. To my delight, I discovered that the growth in my tank during the week had been explosive - all plants had grown considerably with all my stem plants noticeably taller, bushier, my swords with increased root growth and leaf production, and my Glosso and my E. tenellus *finally* sending off runners. The BBA seems to be much better as well (in particular, seems to be dying off of the gravel).
So in a nutshell, this is my extremely simple system - once a week dosing of PMDD macros/micros/phosphate. The next step will be experimenting with mid-week dosing to see if more additions continue to improve growth of plants (though not sure if I can handle more vigorous growth - having enough problem with keeping up with the pruning of the plants).