I’d missed this yesterday, but it appears that those looking to see what the next wave of Exchange looks like have to wait no longer. The first beta of Exchange 2010 has arrive and can be downloaded at http://www.microsoft.com/downloads/details.aspx?displaylang=en&FamilyID=1898ed2c-2f88-48ac-824e-d3d20fad77d7
(Note 64 Bit only, but it WILL install on Vista with SP1 if you want to eval functionality.)
