You will have hard time to got a decent dps as a feral druid. Thats for sure.
But if you have the time and the patience, you can be a really a good dps and the best offtank in the game.
The issue with feral dps is that you have to know all theorycraft about it because there are tricky stuff that dont make much sense at first if you compare to other gameplay classes.
As Aquane mentioned it, shapeshifting is the best dps potential of a feral dps due to the talent and the helmet that can give you up to 60 free energy per shifting ( but it cost mana, so here goes the 2k mana flask and the farm for mana potion / rune ). It makes the gameplay much more complex and totally different from other classes, it also allow different ways to manage your mana pool but it requires some macro to be really effective.
+ damage weapon gear doesn't make sense as a feral does not use his weapon but this make feral dps going sky high.
It is simple, +9 damage on your 2 hand weapon and a +8 from the weight stone, for a total of +17 = +17 dps in cat form = +238 Attackpower only ( this is pretty epic ).
A feral can easily beat a lot of classes in dps, during pre raid gear and early raid progression due to that.
The major problem is that you wont see progression in your dps until AQ gear, as BWL and MC gear are not really cat oriented. Other classes will see their dmg going up a lot during the MC / BWL progression, and yours will stay the same.
There is also the glancing blow problem that you cant solve that will limit you white dps.
Beside all that almost nobody know shit about feral potential as this is so mess up and require a lot of commitment. So you wont get a room easily in a raid guild.
But it really shines in early raid progression, offtanking and when you start getting AQ gear.
So if you seek challenge, you wont get bored to play as feral dps ( not like other classes, @spamming frostbolt ) as it require a lot of time and effort to reach its potential. And the gameplay is unique in its own way !