Tree Bark Jacket, a resto-druid-themed blog that was new to me, has an interesting post up about whether there is such a thing as an entirely bad talent. The author's argument is that no, there is not, the reason being that even talents that are regularly dismissed are still useful sometimes; they're just situational.
On a broader scope, Keeva makes the important point that you can't make all your talent decisions based on Recount or on people's advice from Elitist Jerks (etc.). Everyone's playstyle and raid makeup is different, and every raid encounter is different.
Here's a personal example: It may be hard to convince your DPS to use Lightwell in 90% of fights, but your tanks will love you for it during a Maexxna web wrap. Does this mean you should take it? That's for you to decide. I kept it while Naxx was still progression content for us, and ditched it in Ulduar where I couldn't find much use for it.
In the end I mostly agree with Keeva. The majority of talents in our talent trees are useful in some situation or other, whether it's raid healing vs. tank healing, 5-mans vs. raids, PvP vs. PvE, or what have you. There are a few that are or were simply bad - the old version of Throwing Specialization springs to mind - but nowadays, those are pretty rare.
If a talent looks useless to you, you probably just aren't thinking of the situations where it'll be useful. But that's OK, you should skip the talents that won't help you in your game. That's the great thing about talents: everybody makes their own choices.