x froze up

[pnico]

Hi
Got my replacement x from best buy. Was wondering if there are too many apps open can that cause the phone to lock up if it runs low enough?
What's the verdict on task killer some say it messes with the os others say its good to reserve memory and keep the system running smooth...because im wondering if i had too many apps open that caused it to lock up... ,only happened once... .
Quirky device i guess like any other....

Thanks