Funny you mention it, I had my first broken spoke tonight. I have not had any wheel problems on my road bikes, putting over 4,000 miles on them in the last year and tonight the first time out on a mountain bike that is supposed to have overbuilt wheels and I pop a spoke after 7 miles :/ I will say that it was a pretty rough single track trail with lots of rocks, roots and ruts to negotiate but still I would not have expected a spoke to break. I guess you never know.