I think how often manual trim is needed can have alot to do with a persons specific flying style. Sometimes im in the mood for a night of turn fighting. Or in some instances stall fighting.
When im turning and slow I find myself trimming more often than if im in a pony at 20k. Although as previously stated in a 109 at 20k im always paying attn to trim.
Some planes certianly do require more trimming than others. I think that these planes benefit most from manual trim.
