If you want to use your MacBook as a desktop system, you can connect a USB keyboard (and of course, a monitor), and the internal screen will stay turned off that way. I rarely use my MacBook outside the office, so this setup is perfect for me. It also turns out that the Macbook fits perfectly between the stem and the panel of my Belinea o.display 24" -- which means that it does not use any valuable desktop space at all.
Problem: In order to power-on the MacBook, I had to remove it out of its resting spot, to open its lid which is covering the on/off switch. Not a nice concept, Apple.
Solution: I taped an old PCI slot cover to my MacBook, as shown here: Mounting 1 Mounting 2. The slot cover sticks out far enough, and can easily be bent a little bit (just about 1/4 inch), which presses the button on its other end, inside the MacBook.
Here are some pictures of the full setup: Setup back 1 Setup back 2. Mounting and remounting of the slot cover is a matter of seconds.
Mac OS X Hints
http://hints.macworld.com/article.php?story=20080908013535674