Less weight is almost always good. Whats also good is that you now can get a tent that weighs the same or less than a bivy bag. Thus you can have a little home in the woods in which to sleep, read, and hang out, instead of just crawling into a nylon tube.
Tarptents (tarptent.com) Contrail and Rainbow are both very clever designs. Tarptent takes advantage of lightweight fabrics, single-wall design, and the fact that nearly everyone now carries trekking poles. Their designs use trekking poles as key structural components, so you arent carrying extra tent poles.
The Contrail ($199) is the real weight champ and an excellent tent for one person. It employs a single trekking pole at the tent head, stakes for tension, and small struts at the tail to give that part of the tent some form. Mesh around the base brings in air, which can exit at the peak of the tent before too much condensation can form.
The Rainbow ($215) is a little different. It has a single tent pole that forms an arch from end to end. Then you use your trekking poles to tension the floor of the tent horizontally. That makes it free-standing (remember, the Contrail requires you to use stakes), although of course the Rainbow also needs stakes just to hold the thing down. The Rainbow is a little roomier, and for a mere seven ounces I think thats a good tradeoff.
Six Moon Designs Lunar Solo Enhanced ($235; sixmoondesigns.com) is very similar to the Contrail. The main difference is the layout: The tent/trekking pole for the Lunar Solo holds up one side, and the door is along that side, rather than at the end, as in the Contrail. This makes sense so that when you sit up, youre in the middle of the tent, at the tall spot. On the other hand it might leave some people feeling claustrophobic as the tent tapers down to the floor more or less over ones head. But its hard to argue with the weight.
As for myself, Id probably go with the Rainbow because I like its roominess. But all three of these tents really show what you can do with good design, light materials, and a little ingenuity.