Aaaargh, now you've got me. I don't have the exact weight to hand, but fully loaded I'd say it's about the same as an OC 15l+pony rig. You can carry it around on one arm with ease. It sits very comfortably on your back and balance is excellent.
My software of choice is Proplanner, though I'm experimenting with Decoweenie (for Palmtops) at the moment. DDplan is very popular amongst other box users I know - have a look at Madmole's site -
http://www.btinternet.com/~madmole/divemole.htm
I carry quite a bit more weight than my old OC twinset rig, currently I've got 10kg on board, but that's compensating for a drysuit, lots of layers and plenty of air in the suit. It's coooold here right now. The extra weight is cos the thing is so much lighter than the twinset, and you've got a lungful + breathing loop of gas circulating round the whole time. Bear in mind that during the course of the dive it gets only fractionally more bouyant as you go along, cos you're using very little gas. There's a big difference between the weight of twins/stages from when they're full to when they've been breathed down to 50 bar, so you start the dive very heavy and end the dive neutral. On CC it's not such an issue.
HTH
Rob