This is a good Ability to use to keep Aggro on more than one target. Putting talent points into Ferocity makes this ability very viable for tanking.
The feral talent Primal Fury gives you 5 Rage on a crit in bear form. If you crit on many of the targets from a swipe, you'll get a lot of Rage in return.
Damage-wise, this ability is generally more effective than Maul against multiple targets, especially acknowledging the fact that Maul prevents you from generating Rage on your next swing.
Patch changes
Patch 3.3.0 (2009-12-08): renamed Swipe to Swipe (Bear) to separate it from Swipe (Cat), range increased to 8 yards.
Patch 3.1.0 (2009-04-14): The [Bear Form] and [Dire Bear Form] version of this ability no longer has a targeting requirement and hits targets behind the druid and to the sides.
Patch 3.0.2 (2008-10-14): Now affects targets within a range.
Previously, threat generation was 1.75x damage done. Now the threat multiplier has been removed. However, the increased damage compensates the lost of threat, especially in AoE tanking scenarios.