TapDex and BuddyPop have more features than the Dashboard widget. And don't forget the vehement opposition some people have to anything relating to Dashboard
As for Quicksilver, some people don't need everything QuickSilver (or LaunchBar or Butler) provides; for those just looking for a quick way to access contact info, something like TapDex or BuddyPop is easier to use and has a more-appropriate feature set.
Options are good.
