"Yet" or "but?"

Source: http://www.bbc.co.uk/worldservice/learningenglish/grammar/learnit/learnitv21.shtml

1. Used as a conjunction, yet is similar in meaning to but, but it has a stronger effect on the reader or listener. Compare: 'The sun was shining and there was no wind, yet it was unusually cold.' 'The sun was shining and there was no wind, but it was unusually cold.' There is perhaps more of a surprise associated with the former statement.Note that you can put and in front of yet when it comes at the beginning of a clause, but of course this is not possible with but, so you can say: 'The cyclists were tired and hungry, all but exhausted, (and) yet they refused to give up in their attempt to finish the race.'

For the English teachers or the more linguistically inclined, here is a whole paper on "but." http://papyr.com/hypertextbooks/grammar/adverbial_but.htm