Cmass...there are also a couple other options you may want to look into....volsmcfalls is correct in saying that the Omnia has the task manager that is brought-up by swiping up from the bottom of the Today screen, so you can un-map that and use the camera button for S2U2.
But....for dealing with apps that don't close, a nice little free app called MagicButton does great work (there are others, but I have used this one in the past)!!
http://www.trancreative.com/mb.aspx
If you really want to map buttons, AEButton allows mapping for one, two, and three presses as well as long presses of buttons...allows a lot of uses for each button!! (there is a free version on the download/purchase page, not sure of the differences, but the paid version works well on the Omnia)
http://ae.inc.ru/aebplus.php