Just getting into using it. Until recently I've been using Bullseye and Unique for light handgun loads with cast bullets.
In some of the larger bore straight wall rifle cases like the 45-70 and 444 Marlin, for light loads, again with cast bullets, I had been using light charges of 2400 and IMR 4227 with a filler to take up space. A friend, hs4570 who recently passed away, got me started experimenting with
Trail
Boss for light loads. Again, as of yet, I haven't used it all that much but so far it seems to work well.
I've recently down loaded some rifle and handgun load data from
http://www.imrpowder.com/data/rifle/trailboss-oct2005.php
http://www.imrpowder.com/data/handgun/trailboss-feb2005.php
This info cover a very basic number of calibers but hs4570 had also worked up a procedure for developing light loads using TB and cast bullet for other rifle calibers. I've used his procedure in cranking out TB light cast loads in 303Br. Jungle Carbines, 444 Marlin and 348 WCF. With what little I have used it, it seems to be working okay and I don't have to mess around with fillers.
hs4570 gave me a pound to try and I have since picked up another four pounds on a powder buy through some local guys on HBC.