so i've been planning to do it for a while, but this morning i finally broke down and picked up a copy of creating applications with mozilla.
i've been playing around with it a bit, and so far i'm quite impressed. xul is quite cool, and you really can throw together a nice little gui in little to no time at all. i'm still slogging through some of the available docs on how to create xpcom components that would let me use arbitrary c/c++ code from within xul applications, but so far, it doesn't look that bad.
there are a dizzying number of buzzwords involved with mozilla (XML, XUL, CSS, RDF, XPCOM, the list goes on and on), but despite that, they seem to have really come up with some neat things. if i was sitting down and creating a new application today, i'd have to say it would be quite tempting to base it on mozilla. it seems reasonably easy to work with, and you get all sorts of cross platform goodness (at least for the gui portions of your code) practically free.