I heard that podcast as well, and here is how I plan to mediate that concern in my particular paddock configuration!
My plan (still in development) currently involves 7 earth sheltered animal barns, each surrounded by four paddocks of approximately 1/2 acre each, adding up to 28 paddocks totaling approximately 14 acres. I am planning to have both pigs and chickens together, moving from paddock to paddock and barn to barn, though I do expect that there might be a slightly higher level of impact in the area surrounding each barn, the system will be quite large, and so the area around and inside each barn will still get significant rest. This system will have no "sacrificial" areas as Paul described them in that podcast either, with a lot of flexibility available as to the order of rotation, as from in each barn, one of four paddocks can be selected, or from any paddock, one of several adjacent paddocks can be selected.
The entire area of this paddock system is going to be encompassing a "maze" of very large hugel beds of the Sepp Holzer style, with a very diverse polyculture on all the hugels. There will be wide paths (10' - 12' wide), some of which containing a few "field crops" (such as grains, legumes, etc) in strips between the hugels. I am currently in the process of planning this system and acquiring a nice big excavator to build it with! I'm even getting a tiltrotator to make digging curvy trenches and accurately placing the hugel logs much quicker and easier.
Referencing back to the original poster's question as to pig density, I think Sepp's reply would be to "ask the paddock", meaning to judge the answer to this question by the diversity and maturity of the vegetation in the paddock. In his second book, he references a quite small range of animal density, which (if I recall correctly) 2 - 12 pigs per hectare. I expect to start with relatively few animals and increase them over time as the maturity of the system allows. With as many paddocks as I plan to have in my system, I hope to be able to (eventually!) increase the density of the animals fairly significantly because the length of time they remain in each paddock can be so low.
--Joshua