Interesting! ''.join() has the advantage on longer strings though:

$ python -mtimeit "'aaaaaaaaaaaaaaa' + 'bbbbbbbbbbbbbbb' + 'ccccccccccccccc' + 'ddddddddddddddd'"

1000000 loops, best of 3: 0.224 usec per loop

$ python -mtimeit "''.join(('aaaaaaaaaaaaaaa','bbbbbbbbbbbbbbb','ccccccccccccccc','ddddddddddddddd'))"

10000000 loops, best of 3: 0.201 usec per loop