Beta 4 ever!
A few sites that I use everyday are in Beta; GMail and Flickr spring to mind. They've been in beta ever since I started to use them, and they show no sign of being in a hurry to get out. It used to be that beta was a transitory phase but it's increasingly becoming a symbol of ever changing, ever improving code, almost a designer logo saying 'we're at the bleeding edge'. I think it also makes a good get out clause - 'gmail crashed? Oh well, it's in beta so don't say we didn't warn you.'