Recently upgraded to VS2008 SP1 RTM, as I wanted to try SQL server 2008. VS2008 SP1 is a pre-req for the SQL server installation.
After the installation, I opened my visual studio IDE to see that the intellisense stopped working. After a day's struggle found that the Text Editor->All languages setup was screwed up like below.
Navigate to Tools->options->Text editor->All languages and just un-check and re-check the last three check boxes. Now the IDE behaves as expected.