The latest MSDN shipment finally arrived an in it was a shiny new copy of the Longhorn Beta 1 release (aka Windows Vista). I'd thought about downloading it before, but any MSDN download over 1 Gb I usually wait for.

My impressions first up were from a user perspective (ignoring all the funky stuff under the hood) and it seems like quite a good update to the O/S. Obviously there are other sites that explain it all in more detail and I'd recommend you go have a look at Paul Thurott's site for example.
My biggest problem I had was that IE7 didn't work with my asp.net application. It seems to be something to do with the viewstate or something - I'll have to investigate.

Oh - one big tip - don't install it in VirtualPC 2004 unless you have to. It's dead slow and painful to use. If you've got the disk space make and use a spare partition (eg using Partition Magic) and install to that. The performance difference is massive especially if you don't have truck loads of RAM.