What exactly does the spell that the Seeker casts do? Doesn't seem to do much damage.

It drains your Health, Magicka, and Stamina a bit.

This^ I noticed that it still doesn't do much though, even on higher difficulties.

When I tried the Conjure Seeker spell, it did something like a mini whirlwind at some bandits, and they went flying. Took out their health a little, but the seeker is very, very slow moving.

I agree with Ashley on this one.

My Mage has better luck with the new Dawnguard summons more than he likes the Seekers... the Seekers just don't do much at all except serve as a temporary distraction.

I don't think they're talking about the Conjure Seeker spell, but the spell the Seeker attacks with. What kind of attack it's supposed to be.

It is a mini whirlwind type spell

It doesn't do anything for me, though that may be because of magic resistance.

Bretons, 'nuf said.