Another improvement in the space-to-weight area is the Tarptent Rainbow. It's a single person tent, but is considerably lighter and wider than the MSR Hubba (I chose that tent because they somewhat resemble one another.)

So, why do I prefer the Hubba? Mostly because it's easier (for me) to pitch - a little less fussing around to get it taut. Also, on a hot night, I like the option of leaving the fly off for 100% ventilation - can't do that with the Rainbow. Those are "comfort" choices that I'm willing to sacrifice weight and space for - but I certainly wouldn't try to force those choices on you. The Rainbow is a great tent, and I'd recommend you give it a serious look.

Another reason the Hubba works for me is that I'm not carrying very much gear, so I don't need a whole lot of space. Using nearly all MSR gear (not noted for being lightweight), and a Vapor Trail pack, I'm still only carrying 18 pounds for a two-night summer weekend. My pack goes at the foot of the tent, turning my Thermarest Prolite 4 into a full-length pad while solving the problem of where to store the pack. My shoes go under my head, with my Dromlite (inflated with air or filled with water) on top of the shoes to make a pillow. Water bottle, filter, rain gear (in a stuff sack), spare clothing (a pair of socks), first-aid kit, toilet paper, and map case arrange into the 4 corners of the tent, with a tiny bit of room to spare. The Pocket Rocket, Titan kettle, and food are hanging in a tree.

I ended up choosing the Hubba over the Rainbow for these reasons; I didn't need any more tent. By choosing a smaller footprint, I have more potential campsites to choose from, increasing my chances of camping where I want. So, for me, a solo tent is perfect. If you're carrying more gear, or are more comfortable with the extra room, you'll need a bigger tent. Considering that I began camping when a "lightweight" two-person tent weighed 7 pounds and solo tents were unheard of, I think that all tents today are pretty lightweight by comparison.