I can understand all of the answers against using them here, and I've made them myself, but I want to think about this a bit, so let me give some reasons in favor of using them that you all can trash.
Let's even exclude the obvious like using computer graphics.
1. Words are going to be written on the board (or regular transparency projector for a larger class) at some point anyway. How to spell a name, or just to cue that this is a new or important topic. I don't know any prof who doesn't write down some words for the class. So why does it matter whether they're on a computer projector or just written by hand?
2. With slides, there's an objective record. This is good for two reasons: a) so that if you miss class you can see what happened, and b) so there's no debate about what was covered in class, which can happen around test time.
3. Having spent time at a German University has led me to see things a bit differently. In the US, there's more of a culture of needing to go to class, so there's less emphasis on getting information to students outside of class. I can understand the idea, but in Europe there's more emphasis on students getting the course ideas anyway they can, even if it means working outside of class. If that's your perspective, putting an organized set of information like lecture slides in the hands of students is seen as more desirable than, in effect, making them come to class to get the goods.
4. I think it also depends on what type of class it is. If it's about discussing ideas that come from the students in class, as a way of developing critical thinking skills, debating, and communicating, you wouldn't need lecture slides. If you're conveying new information, that's a different story. In my view of a good class, some new information should be conveyed (the slides), and then the class might use and discuss and ask questions about that information (slides are ignored for the moment).
[edit: oh yeah, and the idea that the teacher doesn't know what they're going to say before they look at the slides, or just read slides to the class, is ridiculous of course. But anyone who's going to do that is also just going to read from notes or read from a book, i.e., they're a bad teacher and whatever method they use is going to be bad.]