The Good: Light, quality construction
The Bad: kinda pricey, but good deals can be found online
SDG's Ti Fly has titanium rails and thin padding to keep the weight to a minimum. I scored a good deal on one and put it on the dh bike where it works great. It is small/thin enough to not be in the way when moving around yet it feels solid when you need it to give the bike a little input with your legs. The saddle has been through a few crashes and the sides have held up well considering I got version with the nylon weave sides that are a bit tougher than a regular fabric.
I've used SDG saddles in the past and am a fan of the Bel-Air for trail riding where you spend a bit more time sitting down. Also the I beam is a really cool technology but I'm glad that SDG makes a railed version of their products.
Overall, the saddle is nice and great for something lightweight and minimal. Not the most comfortable thing for me to sit on for an extended time but that's all personal preference anyway. Despite being more money than I normally spend on a seat, I'd get it again.