Sometimes, if some kind of Automatic Task Killer App is installed on Android phone and if we select all tasks/processes to be automatically killed periodically then it is a big problem. One needs to check setup of those Task Killers. In General, expers do not recommend use of Task Killers becasue sometimes by mistake they may kill required processes on the phone.
Other issues:
Menu, Home, Back, Search keys not responding - Press End Call/Power key once and it wakes up these keys come alive or just pull out physical QWERTY keyboard out and it wakes up these keys.
Notification Bar not responding - Long press Home Key, It displays Apps that are currently running/active on the phone, Press Back Key and now Notification bar can be pulled down
3G Data not working - Long press End Call/Power Key, it brings up Power Menu, Choose Airplane Mode on, Phone shows Airplane Symbol in Notification bar, Wait for 2 minutes, Long press End Call/Power Key, it brings up Power Menu, Choose Airplane Mode off, Airplane Symbil disappears from the notification bar, 3G Data should come back
I recommend to have at least 50 MB RAM free on the phone at any time. I use Android Assistant App which allows me to monitor how much memory is free and how much is in use. It allows Quick Boost to free up RAM. It also has Auto Boost option where it periodically kills Apps/Processes based on our selection (One need to exclude System Processes from the list). Also, I use Go Launcher EX Home Replacement Screen. It allows me to see what Apps are running on the phone and I can close not needed Apps gracefully.