Mobility as it stands in DDO pretty much seems a wasted feat slot, only taken to qualify for other feats.
in DDO: Adds a +4 dodge bonus to Armor Class while tumbling.
in D&D: Adds a +4 dodge bonus to Armor Class against attacks of opportunity caused when moving within a threatened area
suggestion: Adds a +2 dodge bonus vs melee attacks while moving, and additional +2 while tumbling
note: I specified against melee attacks because ranged attacks don't provoke attacks of opportunity (which don't exist in DDO anyway, so it's a moot point, but I thought it was closer to the spirir of the original mobility feat than what we have now)