Pros: great insulation, stainless steel
Cons: hard to drink straight from the bottle
As many other reviews have noted, the bullet bottle keeps hot drinks hot and cold drinks cold for hours on end. It's got some great insulation. My wife and I each got one for christmas - I'm not a coffee drinker, so I usually use it for smoothies in the morning, while she uses it for coffee or tea. Once I finish my smoothie at work, I wash it out and fill it with water for the rest of the day.
It's also a good tough bottle, you don't have to worry about any potential contaminants from plastics, and it's pretty stylish. My only complaint is that it's not easy to drink straight from the bottle. It's really meant as a thermos, and you can either use the cap as a cup or pour the contents into another cup/mug/glass/etc.