When Vista was announced, it was said that it will be last 32-bit operating system from Microsoft. With Windows 7, they changed their mind since Windows 7 will come in both 32-bit and 64-bit flavors.
Server platform took different approach and Windows Server 2008 R2 will come only in 64-bit variant. There will be support for 32-bit applications (WOW64) but underlying system and hardware will work only in 64-bit space.
Once server goes that path, client platform will follow. Windows 7 may be known as last 32-bit Windows.