Co - and Adjacent channel interference has been discussed on these forums and others at length.

You start to experince issues with interference when you have a good amount of traffic on the network (same channel or adjacent). I have conducted my own study of this a year ago or so and what they say about your throughput being half'd is true.

think back about 15-18 years ago when you used a NEW cordless phone and at times you would listen to your neigbors conversation. Same holds true with 802.11 wireless. If you use the same channel within 25 db you will likly see some throughput issues. One APs traffic is another APs noise.

Thus why standard reads 22 Mhz from center spacing between channels, so to avoid interference.

Your channel situation at your house and you dont see issues. if your neighbors start using the wireless (exmaple downloading an ISO) and you start using the medium as well run a analyzer and check out your retrys.

Specific to your question, what are the wireless users using via the wireless (web surfing, data applications, VoIP over wireless) ? This will really dictate the shaping of this ...

best pratice is you dont want to exceed 20-30 clients per AP. You could shape the RF with patch or direction APs to limit side exposure interference.