It is known that the type of computing power required for mining is the same used to generate addresses, and it is known that "in general" it is much more profitable to simply mine, rather than try to generate addresses hoping to stole their content.
But AFAIK there are some addresses out there which contain a huge amount of bitcoins: successfully generating their private key would award you a lot more bitcoins than those you would get generating a new block.
Has someone actually made some figures comparing the average revenue of mining vs. the chance of generating the key of a very rich address?