Quoting slugsgomoo:
if you're getting very low vacuum (inches of vacuum, pounds of boost /ubbthreads/images/graemlins/wink.gif), it means you probably have a pretty severe boost leak somewhere. Have you boost leak tested? are your readings different off the manifold than they are off of "P"? If they are, that's an indication of a problem as they should match exactly.
For what it's worth I think I'm ~ 17inHG at idle with HKS 272/272 cams, stock should read a bit more vacuum than that, bigger cams a bit less.
Kelford 272's here. 11-12inHG seems to be pretty standard for what i have.