Admittedly, I jumped on the bandwagon for these back in April. I started by using approx. 75g of Phosban on my 65 gallon reef. Some nuisance algae that I couldn't get rid of died under the Phosban treatment. When the media became exhausted, I switched to a similar amount of ROWAphos media. The rest of the nuisance algae died after about a month, but my SPS corals all started browning out. I then switched to carbon, and feel this has done my tank well.
I'm putting together a 29 gallon tank right now, and am going to try a small quantity of Phosban (I think the ROWAphos media was too efficient; the Phosban stripped the phosphates out of the water slower) and see what happens.
In regards to how much media to use, I think a little less than 1g of media per gallon is a good starting point.