404's after changing permalinks in 3.2.1

So I updated a blog to use just the post name instead of the year/month/day format … My understanding with this version of wordpress was that no further 301 redirects etc were required and that wordpress would redirect accordingly however that seems not to be the case if I enter year/month/day format I’m getting a 404.

If I was mistaken I apologize can someone tell me the best way to go about this?

Thanks in advance.