Richard Lenski has been breeding 12 separate strains of E coli for upwards of twenty years now; over 44,000 generations. In one of his strains, the E coli developed the ability to eat a substance present in the environment, but previously inedible to E coli--citrine--at around generation 33,000. This appears to have required the previous accumulation of a series of otherwise neutral mutations, until, poof! A new function!
Read about it here.