The North Face Beeline 30 Degree Sleeping Bag

The perfect ultralight 30-deg - for me
No zipper = no drafts, as mentioned by Kevin Hedahl. I personally never let my dirty skin touch my bag, as I sweat too easily, and that would ruin it quickly. So, if you follow this practice (socks & undies, or better yet, bag liner), you'll do fine. In & out of the top is easier than it seems, and the zippered foot box is The Bomb for keeping me comfy. Love it!!!

Great plus 30 bag
I just used this bag on a 3 week July mountaineering trip in the NW including one snow camp/climb. In a tent, the bag is comfortable and warm with a single pad down to 30 deg and on snow with 2 pads (closed cell plus a thermarest). I suspect that this bag would be a good lightweight bivy setup with the addition of a bivy sack and down jacket and pants. Will try this option soon. The zipper at the foot is a great option and the bag stuffs down to a very small volume.

Fantastic bag for ultralight summer trips
I purchased this bag in an effort to lessen the weight for a weeklong trip in the Marble Mountains, CA. I am 6' and purchased the long bag. I fit into the bag with room to spare. The temperature dipped to approx. 40 degrees at night. I slept in a two person tent with my girlfriend. Using a closed cell sleeping pad, a fair amount of cold seeped through. With an inflatable, open cell pad, the bag would have been incredibly warm and would fully meet its 30 degree rating. Not having a zipper didn't pose much of a problem. It wasn't difficult getting into or out of the bag. No zipper means no draft, which was fantastic. The zipper at the feet provided good ventilation on hotter nights. The bag is made with very lightweight nylon. I didn't have any problems with tears. However, the material isn't terribly comfortable on bare skin that is dirty and sticky with sweat. A couple days into the trip, I had to wear clothing to sleep comfortably. Overall, I highly recommend this bag for any wanting a lightweight bag.