What happens if www cannot connect, how long does it take before it times out. If I use yield will it just hang if it can’t connect or will it timeout eventually?
See the example of WWW.error they toss in an invalid URL (i.e. something that will no connect). Yield will allow other code to run, if you have code following yield on a WWW that you are expecting to run while the WWW is connecting then your code structure needs to change to support WWW connection and results as asynchronous.
http://docs.unity3d.com/Documentation/ScriptReference/WWW-error.html