I just installed Windows 8 but had a hard time figuring out why not all sites were available. I quickly found out the DNS lookup failed.
Since I had to uninstall my ThinkVantage WIFI manager before installing Windows 8 I assumed it could have something to do with an invalid configuration.
I had to reset my TCP/IP stack before I got it to work which is done using
C:> netsh int ip reset reset.log
C:> netsh winsock reset catalog
It should do the trick — you might have to restart your computer.