My school recently announced that in the fall we will switch to a system where evaluations will be conducted online. I am against this for several reasons. For one thing, it means that students who barely attend class have the same chance to evaluate me as students who attend every class. But since students with poor attendance records have a poorer basis for evaluation and are likely to be doing poorly in the class, so their evaluations of my teaching are likely to be both bad and based on insufficient information.
For another thing, it means that I cannot control when evaluation day occurs. As an anonymous commenter recently pointed out, you should never conduct evaluations right after you return a major assignment. I no longer have any influence over whether my evaluations are conducted right after I have returned anything.
It also undermines my ability to more directly control their mood on evaluation day. Before I pass out the eval forms, I like to say a little bit about how much I enjoy teaching, how I approach my role as teacher, and how much we've accomplished so far in the class--I try to emphasize that we've accomplished a lot. I also emphasize that I take my evaluations very seriously, and how helpful I have found them to be in the past. I point out that on several occasions, suggestions that appeared in evaluations have directly resulted in clear improvements in the class, and I give an example of one such change. Then, in keeping with anon 9:43's suggestion, I tell a joke. Unlike 9:43, I make no effort to smoothly integrate this joke into the lecture. I say, "and now, here's a joke!" and then I tell the joke, get a big laugh, and leave the room.
Now I can't do any of that.