I was just playing around with CE 1.8 and tested how many of the more important modules (catalog, checkout, sales, ...) you can deactivate without running into apparent problems. Turns out: pretty much all of them.
I'll put the list of my deactivated modules here just in case I want to move my blog from WordPress to Magento sometime. :P
This would be a healty base for general purpose websites. If you want you could disable even more modules.