Mostly in line with earlier rumors, Twitter has confirmed that media and @names in replies won't count toward its 140 character limit before too long.
A source previously indicated links wouldn't count either, and while that's not specifically pointed out by Twitter in its blog post, it does say it's "exploring ways to make existing uses easier and enable new ones, all without compromising [the service's] unique brevity and speed."
Other changes include the ability to retweet and quote yourself with a simple button click, and new tweets (not replies) that begin with @name will reach all of your followers, eliminating the need for the ".@name" workaround. The latter is good if that's what you want, but bad if you want to privately ask a question, for example; hopefully Twitter creates an option to enable or disable this behaviour, whether per tweet or globally.