Simon wrote: I try to carry my ballast closer to my center of gravity.
Simon, are correct that carrying ballast low tends to dampen the weight shift authority and make the glider harder to turn. Break pressure is proportional to loading, so even with the ballast loaded high, the breaks will still feel heavy.
15 years ago, all the comp pilots flew large gliders and carried a lot of ballast because there is an efficiency of scale. L/D improves with size for the same loading (pounds per sq foot) because the parasitic drag is a large component of total drag in a PG and it doesn't scale linear with the size. Big guys will glide better then light girls in calm air. It's a sexist sport.
Optimally, you want to be able to dump the ballast in flight, and some harnesses are set up to do so, but not mine. I was carrying the ballast high in my back storage the other day, but it didn't work well. I carry it in the same place on my tandem harness and that works ok. I have two 10Kg bladders, specifically marketed as ballast bags, but you can also use them as general water bags when camping. They come with a shower hose kit. I sometimes fly with both bags when I have a light tandem passenger. If so, I have to put the 2nd bag on the passenger, which I don't like to do because it makes it hard for them to run. In addition to occasional extra ballast, I normally fly with 2 liters of water, and sometimes 3 in the summer.
I think most pilots have gotten away from using ballast for a number of reasons. It makes ground handling awkward and there are issues on a hard impact. I've gained 20 pounds over the past 5 years, so I've got build in ballast now.
You can also check my notes on wing loading from 2002 at
http://paraglide.net/comment/02/wing_loading.htm