Energy usage (ie. battery life) has been brought to my attention recently. As can be seen above, OpenTTD running in background doesn't handle things nice and battery drain is much greater than it should be.
The average value for "OpenTTD running" is 1,07W, for "OpenTTD in background" it's 0,51W and for "Idle" it's 0,11W.
Other Symbian SDL ports also will have this problem. So, quick advice: don't leave OpenTTD, C2Doom, ScummVM running on the phone in background, your battery will die very quickly if you do so.
Edit: The background energy usage of my SDL's port has been reduced to 0,13W.