Using 4 Channels in a Multi-Accesspoint Environment

Found this paper: “Channel Overlap Calculations for 802.11b Networks” by Mitchell Burton from Cirond Technologies Inc. (It was on slashdot last year, but I must have missed it)
Popular opinion states that you can use only 3 non-overlapping Channels for your WLAN: 1, 6, 11. This paper concludes that the interference by overlapping channels is less affecting than the problems with modeling a 3D building with only 3 channels.