At present the bulk of my problem seems to be related to Time Machine and the iMac putting itself to sleep (when not set to do so).
However, with no USB drives plugged in and all is fine.
Plug USB drives in and no Time Machine it connects to Airport Extreme OK and no problems but it then seems to go to sleep very often, a lot more than it is set to and also puts my printer to sleep, it didn't under SL. You can sit and listen to the computer shutting down and then seconds later starting again without touching a button. It does not do this if there are no USB drives connected. It does it whether the button for putting drives to sleep is checked or not in the network settings.
Each time it powers back on, I have not done it does it repeatedly on its own, it renames the iMac saying the name "iMac" is in use. So I start with plain "iMac", next it becomes "iMac 2" and so on. Yesterday I was out for a few hours and left it switched on, when I got back it had got to iMac 856. Thus it had gone to sleep and woken up of it's own volition 856 times. I do not know enough about operating systems to know where to start to sort this but sure did not have this problem with Snow Leopard.
It get worse if I put power into Time Machine, even if it's not set to be used, just merely switching on and then Lion does not like Airport Express. I lose my WiFi connection in Express and yes I have checked that the Time Machine is not configured to be a wireless router in it's own right.
So no USB hard drives connected it works OK.
Connect USB hard drives, WiFI is OK but the computer keeps switching itself off and on again (sleep mode).
Power up Time Machine and I lose the WiFi.
Richard
Richarud.