I hate laptops at the gaming table!!! I swore I would never do it. They are a horrible distraction, they take up too much space, and the cords are a trip hazard.
Here comes the but....
They do have some very valid uses for a Dungeon Master. Especially if you are DM'ing outside your home.
I am a D&D Insider subscriber so having instaneous access to the character and monster builder is a huge plus.
I play background music during my sessions, which is stored in my iTunes library.
But I recently found something that put me over the top. It's called the Dungeon Master's Battlescreen.
For the first 11 months of DM'ing 4th Ed. I was overwhelmed with all the bookkeeping. Hit Points, Ongoing Effects and Initiative not to mention all of the Monster and PC stats. In short I wasn't having a whole lot of fun.
DM's Battle Screen does all the dirty work for you.
Seriously, I could go on and on, but you need to see it for yourself. The program is Freeware and not an official WOTC program. You can however import files from the Monster and Character Builders. Take a look.