Overall a good article, although the claim that "WiFi has 11 channels and can give you 220Mbit in the air" is just wrong. You'll never deploy on all 11 channels without causing massive adjacent channel interference. 802.11 likes 25 MHz per AP, and the 2.4GHz channels are only 5 MHz apart. Deploying on anything other than 1, 6 or 11 will cause more problems than it will solve.

Additionally, dismissing the 5 GHz channels by claiming "those have lots of issues with many devices" is a facile argument. Deploying 5GHz channels (of which there are many more than 2.4GHz) is an excellent strategy in many cases - it enables you to offload 5GHz-capable clients (laptops, tables) from the 2.4GHz radios, freeing them up for 2.4GHz-only systems (smartphones, old laptops).

Anybody looking to deploy WiFi at a large conference needs to read Aruba Networks' High-Density Validated Design Guide, regardless of the hardware vendor you choose:

http://www.arubanetworks.com/pdf/technology/DG_HighDensity_V...

Appendix B and C contain some excellent information on planning and theory.