1. All devices in the house will lose connection to the router. Router will not scan in Airport Utility. Hard power reset required.
2. I have one 24" iMac about 10 feet from router connected over wireless. Over time (like a few days) the internet speed will drop to about 1mb/s even though the connection info in Airport Utility from my other mac shows this mac wireless is connected at full g speed. Other devices in the house internet speed is normal at this time.
3. I have one iphone (out of 3) in the house that will just stop connecting to the router (regardless of distance to it). A reset of the phone does not fix the problem, however a reboot of the router does. Other devices in the house at this time are connected fine.
These are all classic symptoms of wireless interference that is causing interuptions and stabilty issues on your network.
Cordless phones, other wireless networks, wireless camera/security systems, televisions, satellite receivers, wireless mice, wireless keyboards, and any number of other electronic devices can cause these problems.
See this Apple support document for more information and some possible fixes: