One little detail that most people forget to mention.
Paris window-boxes like this one are filled with flowers all year round. Yes, even in February, even when the month isn't as mild as 2007 has been.
Evidently there is never enough of a hard frost to kill off the hardier potted flowering geraniums, cyclamen, etc. And with the ambiant heat from the vast single-glazed window panes, it's a virtual greenhouse.