I chose it primarily because I play table tennis and so I have a lot of friends who are Chinese. It's also helpful when playing against Chinese who think you don't understand their spoken comments to each other in doubles :-) It's also very interesting to study a language that isn't a Romance language, to see how a truly distinct language evolved and to see the differences and similarities that still exist.

Spoken Mandarin is actually very reasonable to learn. The grammar is logical and there's not a huge number of words to learn like English. People often make a big deal about the tones, but I think the concern there is overblown. I'm sure I mess up tones all the time, but I'm also sure a native speaker won't be confused by my mistakes (they haven't been so far, at least, as long as I speak a sentence instead of just one word because they can figure it out from context).

The pain comes when you're trying to learn the essentially non-phonetic written language (yes, there are "radicals", but don't get me started on how inferrior that is to a truly phonetic written language). I've studied the written language some, but I don't have any real goal to learn it well, except where it might help me with the spoken language.