How do you code review?

At some point in your developer career you'll have to do a code review. It seems everyone does it differently. I spend about an hour on a code review. Any more and my brain is toast. I also have a checklist that I run through:

• Are there any style issues?
• Does the code placement make sense?
• Is one method doing too much?
• Are there tests? If not, should there be tests?

How do you perform code reviews? What's worked well for you and what hasn't?