A colleague sent me an article from The Washington Post, "Wide Web of Diversions Gets Laptops Evicted From Lecture Halls." 
The article described the banning of laptops in various courses, including David Cole's Georgetown Law class. According to the article, laptops in the classroom have " .....evolved into a powerful distraction. Wireless Internet connections tempt students away from note-typing to e-mail, blogs, YouTube videos, sports scores, even online gaming -- all the diversions of a home computer beamed into the classroom to compete with the professor for the student's attention."
While I understand the impulse to ban laptops from your classroom, I'd argue that you'd be giving up far more than you gain. Laptops are a tool, and all tools need to be utilized correctly.
Faculty have a total right to control what happens in the classroom. If a faculty member says "lids closed", then her students should close their laptops. The minute faculty lose the ability to control the behavior in the classroom is the point at which teaching and learning effectiveness stops. With this authority, however, comes the responsibility to use it wisely.
A total ban on laptops is a bad idea because laptops can be a marvelous learning tool within the classroom. There are many instances where having your students utilize their laptops will accomplish the active learning that faculty would like to promote. Students want to use their laptops, and you can turn this desire into opportunities for learning.
Times When You Should Say "Lids Down":
a. When you want your students to listen and absorb.
b. When you want your students to participate in conversation.
If you are going to say "lids down" on a regular basis (and you should), you should think about using a lecture capture system. Recording your lectures and sharing the recordings with the class will remove the student rationale and desire to take notes with their laptops. They can take notes later with the recorded lecture. You should make clear to them why you don't want laptops during listening or conversation times, and also be clear about why you are providing them with your recorded lectures.
Times When You Should Use the Laptop:
a. For instant team research and authoring assignments.
b. To provide real time feedback for student presentations, lectures or guest lectures.
c. For in-class blogging about the subject matter you discussed.
One method is to lecture for 20 minutes (with lids closed), followed by a quick "laptop" assignment where students need to quickly answer a question you have assigned (that may require some Web research), and make and post a quick PowerPoint to your LMS. You will be amazed how quickly students can produce a rapid presentation in 10 minutes. If you read John Medina's Brain Rules,  you will discover that retention falls off dramatically after 20 minutes, and that you need to break your lectures into chunks and allow your students time to reset their brains. A quick Web research and instant presentation project is a great way to prepare your students for the next round of lectures, as well as an opportunity to give them a chance to consolidate the information in the lecture materials.
Another idea is to have students blog (using the blog feature in your LMS) a quick set of follow-up questions to your lecture material. You can next display these questions using the projector, circling around back to your lecture. The built in blog feature in a modern LMS is a wonderful tool to allow rapid student authoring and sharing. Having your students write up quick blog entries is a great way to allow them to surf the Web for a few minutes in the service of learning the concepts and facts that you are teaching.
What is important is that you are chunking the delivery of your lecture content and giving your students a chance to "re-set" their brains. After 10 minutes of doing something active on their laptops you can again say "lids down" and deliver the second (20 minute) part of your lecture. A 50 minute class will go much faster for everyone, and I'm betting you will have much higher levels of retention.
It is always better to leverage a tool as opposed to banning it. If you ban laptops today you will find students surfing the Web using smart phones tomorrow. Much better to utilize the tools that students want to use in a way that contributes to your teaching goals.