How should I use a laptop in class without distracting others?

Professors don't share the same rationale so mileage may differ. Usually, the younger ones are more forgiving. Those born before late Generation X (aka 1970 or before) are more likely to feel awkward because in most of their education life, portable computers had not been made popular. So, personal computer and laptop were/are much less integrated into their daily life.

In fact, it's not the laptop, it's what the laptop being used for and the manners of the owner's. Here are some guidelines, most are in my syllabi as well:

• If the syllabus does not require a labtop but you'd like to use one, inform the professor through e-mail for permission. This step, however, can be skipped if the majority of the students have started using one since the beginning.
• Sit to the side or back so that your screen will not interfere with other students' line of eyesight.
• Mute all sounds.
• Be courteous about where to plug your charger and make sure no one will trip over the wire.
• Type quietly.
• Refrain from doing anything other than tasks related to the materials being covered (no Facebook, Reddit, Youtube, games, porn, jokes, e-mail, IM, shopping etc. even you think you have nailed down the contents).
• Occasionally establish eye contacts with the professor.
• Ask questions, keep engaged.
• If there are very few students and the interaction becomes more of a meeting, angle your laptop to either or your side by about 40 degrees so that it's not becoming a wall between you and the professor, or you and other students.

I also ask my TAs to sit at the back of the classroom so that I can make sure karma finds its way when I tally up the in-class performance portion of the final grade.