The jury is still out on this one. Some research suggest that comments are favored by Panda, but you run the risk of getting hit with a penalty if the comments are low quality (which is a hard thing to control).
There are many debates about this. But if you are running a blog, i think comments are good. Without comments, a blog isn’t really a blog. To me, blogging is not just about publishing content, but also the two-way communication and community building aspects behind it. So we should allow visitors to have their voice be heard if they choose to speak.