I agree with everyone else, Windows Vista needs more time.
I installed Windows Vista on a second partition on my computer and use it as my main OS (my other OS is Windows XP). Sure it has a few buggy behaviours, but I think most people here are quite pessimistic. Don't get me wrong, I think Patchou (and many others) know what they are on about.
I think that if someone doesn't have a reason (e.g. not a Developer, Technician or extremely eager to try the OS) to install Windows Vista Beta 2, then they shouldn't. Their computer works fine now and will for a few more years.
If Microsoft releases Vista too early, it will probably turn out like Windows XP (before SP1) did. If there are too many early adopters, this could be catastrophic for Microsoft. But i'm counting on the fact that if Windows Vista is released too early, not many people will upgrade at first anyway because people will be saying that their XP computers are fine just like in the days of 98 when XP was released. I hope this is the case for now.
Windows XP will be fine to use for a few more years so people who are happy with their computers need not to install Windows Vista. If you really want to get Windows Vista (or if you are using 2000 or earlier), wait for a few months and then use your good judgement.