This stacks with the Subtlety talent Camouflage. Contrary to its description, Camouflage actually reduces the speed penalty of being Stealthed, rather than giving a boost in speed. With maxed ranks in both talents, your speed while Stealthed is reduced to 97.5%.
Many raiders skip this talent despite that it actually is a DPS increase. The less time you spend running away from fire, poison, oozes or other unhealthy stuff, the more time you spend attacking the boss.
Patch 2.3.0 (13-Nov-2007): Now increases movement speed by 8/15%, up from 4/8%.