Here's an update for 2008. I closed my pool last year late, waiting for the temperature to get down below 55 degrees. I did exactly what was recommended, including adding polyquat for the first time. We had an extremely long wet winter & spring. I finally opened my pool in late May and the water was clear enough to see the main drain. However, all chlorine was gone and the water was just starting to cloud. I added 1.5 lbs of CYA, 3 bottles of bleach and started the pump. I tested for borates, it was still 50 ppm.
We didn't swim until the last week of June (I'm a sissy when it comes to water below 78 degrees), but I have had zero algae, and used about 1 bottle of bleach per week to keep the water crystal clear. Only needed more when cottonwood trees were covering everything, this year was really bad because of the excessive amount of rain. We passed the yearly rainfall average by the middle of June.
Do borates inhibit algae growth? Yes.