Opera has always been a decent enough browser, but its $30+ fee (or ad-feeding free version) has been a major turnoff to anyone wishing to switch from IE. You could always pirate it, sure, but pirating is no fun; at least if you have a conscience.
Now, Opera has become free (as in beer).
I still prefer Firefox, but now you really, really, really have no reason to use Internet Explorer anymore.
UPDATE: Since Opera’s getting somewhat Slashdotted, why not save their servers by downloading via torrent instead?