According to Microsoft, Windows 8 will be easier to use and faster to install! Windows 8 has a revamped install process and will install in only 21 minutes on a clean system. Until we are able to verify such statements (second half of 2012) Microsoft will continue to improve reliability while also improving the installation experience and raw performance. PCs capable of running Windows 7 should be able to handle Windows 8 flawlessly. Microsoft states that there are currently more than 450 million PCs that will be able to run Windows 8, but we expect that many systems running Windows Vista and even Windows XP will also be eligible.
Read MS blog post here - http://blogs.msdn.com/b/b8/archive/2011/11/21/improving-the-setup-experience.aspx