Kaitie, did you individually tailor these (in terms of having a line or two saying why you were approaching the agent)?
I addressed each to the agent's name, but I only personalized if I had good reason to. I feel inauthentic saying, "I think you'll like my book because you represent my genre" or something of that nature. If my book was similar in nature to something else said agent represented and that's why I chose him, then I would include that, but this only happened a couple of times. Otherwise, I always mentioned if I was a follower of a blog or something of that sort, but again only if it was a legitimate influence on my submission.
There were actually quite a few that I wanted to personalize, but the reason I didn't is because I've seen agents say that it doesn't really help unless you have a reason that's specific enough to be worthwhile. For instance, "I love your blog" might not get me very far because for all they know I'm just saying that, whereas if I can say specifically, "I read your blog often and comment under the name (whatever). I particularly found your post on (something) helpful." Actually, in this case I tended to make a joke, but that's just me.
That's also why I didn't always personalize--because sometimes I didn't know if the person would get my humor or not.
So uh...yeah, long rambly way to say: generally speaking, no.