[endtime]

> Parse trees are cool to look at, but what can I do with them?

One really simple and obvious thing is word sense disambiguation. Plenty of homonyms are different parts of speech (e.g. the verb "lead" and the noun "lead"). I'm sure there's lots of more sophisticated stuff you can do as well, but this might be the lowest-hanging fruit.

[gattilorenz]

However, for that you just need PoS tags (which is also provided by this Google thing, yes). And of course the hard part of WSD is detecting whether "bank" refers to the bank of a river, or the financial institution, or the building where the institution is located, or [you name it].

I use parse trees as a kind of "advanced language model" for when I need to replace a word in a sentence (see for example: http://www.aclweb.org/anthology/P13-1142 ), it's so much better than using just simple n-grams.