We haven't needed 6 PCI slots ever, except for the very few who stack their systems out with really smart stuff. Right now I've my modem, network, sound and SCSI cards in and there's still 2 free; with a more integrated mobo I certainly wouldn't need this many. That's leaving AGP aside.
Given that this PC is about 16" tall, I expect that my next one will be about 7" tall, with firewire, 2x LAN, 6ch audio and DVD-RW over what I have now, aside from the next fast cpu. It's about time PCs weren't such huge beige boxes.