Attack Power is increased by the formula: (Strength x 2) + Agility + (Character Level x 2) - 20
Cat Form's damage and DPS isn't affected by the currently equipped weapon (except by the contribution from Agility, Strength and straight attack power). Similarly, attack speed in Cat Form is always 1.00 unless modified from haste rating.
Procs from "Chance on Hit" enchantments on weapons, since Patch 3.0, now work while in Cat Form. This includes weapon enchantments, such as Mongoose, and temporary weapon enhancements, such as Windfury Totem.
Generates energy via 2 ways only: 20 energy every 2 seconds or the talent Furor.
Cat Form uses Energy instead of Mana and can stealth, like a Rogue.
Cat Form has an innate threat reduction component. This is currently believed to be at 29% reduction, which mirrors the threat reduction of Rogues. (see Threat per Class)
Blizzard has redesigned the Cat and Bear forms and they will be released with Patch 3.2.0. These will have 5 different fur colours, designated by your hair colour (Night elf) or fur colour (Tauren).
A druid in Cat Form can use both stealth and Track Humanoids to ambush people in PvP. By default, if you have no profession tracking on, when you shift into Cat Form, Track Humanoids is automatically activated once you have learned it.
Note: If you're tracking repair or other helpful NPCs or mailboxes, Track Humanoids will override this. When you shift out of Cat Form again, the icon of Track Humanoids will remain due to a display bug, but actually you're tracking nothing then, until you select something or shift into Cat Form again.
The Feral talent Feral Swiftness allows a Feral druid to travel at 15-30% speed in the levels before you obtain Travel Form, which cuts down greatly on downtime through traveling until then.
Cat Form also has an arsenal of difficult-to-remove physical DoTs (like a Warrior's Rend) which can be used to tear casters apart in PvP.