I have a grand Aussie saddle that I could never part with even though I can't use it anymore. I used to use the saddle on a lesson horse but now that I have my own horse and a different barn the tree is to wide for him so I can't use it. It is absolutely the most comfortable saddle your bum will ever rest in. I used to ride all day long in that thing and feel like a thousand bucks after. As far as light weight, Aussie saddles can range between 20-30lbs depending on the make but rarely heavier than 30. I say most are about 27lbs. Mine is about that much and so is my moms and my friends barn's saddles are around there too. They are lighter than some and most western saddles (that aren't synthetic anyway) but quite a few good pounds heavier than any English saddle.
Aussie saddles can come with either horns or no horns, English style stirrup irons or western style stirrups. Some come with fenders and some come with just leathers. The cantle is usually 5" deep and the pommel and horn are more on the short side. The Australian saddle is the only saddle originally designed for a riders safety. The more western style saddles are typically called "Stock Seat." I don't know too much about them but here's some pics anyway. The rigging goes both ways and there's even an "Aussie" way of rigging that is way beyond me. I prefer the western rigging style.
HORN W/ IRONS http://www.saddleteam.com/images/stocpolaussa.jpg
HORN W/ WESTERN STIRRUP (I want this saddle!
HORNLESS W/ WESTERN STIRRUP http://www.paylesssaddles.com/images/1010_small.jpg
HORNLESS W/ IRONS http://www.horizonusedtack.com/weste...e/300319lg.jpg