I've read of people doing it before, eg
http://www.flickr.com/groups/2519165...7614568400032/ but I have yet to take my own flats.
I imagine it'd be difficult to get even if you're just holding the laptop there, and white light is not good if it leaks at a dark site get-together.
[edit] I see Al has posted a link to one here on IIS. That's the one I was looking for but couldn't recall where I'd seen it.