"I agree" LOL
Okay, I couldn't resist. I know in my prior classes (and hope in my future classes) that I agree statements are not acceptable as replies. It isn't as if you're sitting in a room having a discussion and can see head nods and shakes or eyes rolling. Discussion boards are just that .... discussions.
If I have an issue reading someone's post (usually because their grammar or sentence structure is so horrendous I cannot figure out what the heck they're saying), I move on. If I agree with their post, I state the reason I agree. I may agree with 90% of their statements and need to state what I agree with and WHY I agree. Sometimes the post will bring up a question to consider or make me think of another point, in agreement or disagreement, that might need to be brought up.