Making Light points out how unlikely it is to be able to make something dangerous enough to blow up a plane. I've seen at least six other blog posts (while casually skimming) that made the same point: it's not as easy as the movies say it is to make liquid bombs.
And, of course, if it was that easy, then having everyone dump their liquids into a single vat when going through security was a momumentally stupid move.
Lots of other good stuff in that Making Light article, by the way. Check it out.