On our classes hiking trip, we were faced with a lot of rain on the second night. When we were settling into bed, I noticed that my sleeping bag was soaked all the way through. This forced me to share a sleeping bag with one of my tentmates. I found this article, Choosing a Sleeping Bag, and decided I should probably read it.
The article first explains temperature ratings, then the difference between different shapes of sleeping bags (mummy, barrel, and rectangular). It then explains the importance of the shape of the head and the feet of the sleeping bag. It even explains the importance of the zipper and inner construction methods of a sleeping bag. It's very specific about each detail and aspect of a sleeping bag.
I now know that I probably should have brought a mummy bag, or at least a barrel bag along on the hiking trip. The next time I go anywhere, I will probably refer to this article when choosing or buying a sleeping bag to bring. I would recommend this article to anyone who doesn't have a sleeping bag or doesn't know which type of sleeping bag to use.
Mountain Equipment Co-op. Intro to Sleeping Bags, - 'Choosing a Sleeping Bag.' http://www.mec.ca/Main/content_text.jsp?FOLDER%3C%3Efolder_id=2534374302887295