Since I upgraded my VS2008 Beta2 to the RTM, the intellisense has not been working. I have seen a few posts about this, some suggesting you need to reset the configuration by running
devenv.exe /safemode
(see http://msdn2.microsoft.com/en-us/library/ms241278(VS.80).aspx)
but this did not work for me.
So I had a poke about in Tools|Option and found that on the Text Editor|All Languages that the three checkboxes for Statement Completion where showing neither empty or checked but a fully coloured box - which usually means an unknown settings. So a set these all to checked (a tick) and my Intellisense started working.