I had when teachers use projectors or powerpoint to lecture. It's a lecture; you should be writing stuff on the board. If there's so much stuff to write that it's not efficient to write it on the board, you probably shouldn't be displaying it anyway.
I have been attending and giving lectures for quite some time, and in my opinion slides can easily be overused, but the board can be too.
For instance, large drawings are nice to have in slides. Animations are also nice and they just don't work on the board. Visualization of functions in 3d, for instance, usually take too much time to draw "on the fly", and they don't look as nice. Also, if you are teaching programming, especially functional or logical programming, changing the code and showing the output on a projected screen is WAY better than writing it on the board.
Of course, having a slide with equations to do a proof or a solution to an exercise is usually pretty bad, because sometimes the audience will have the ideas in a different order, or a different implementation, and you want to follow that instead of squeezing them into your previously thought proof. If you are not trying to engage the audience into building the proof/solution with you, you are doing it wrong.
That being said, I tried to get a parallel degree in philosophy while being an undergrad in CS* and there were lecturers that used no visual aid. No slide, no transparency, no writing on the board, no nothing. That was enough for me to leave the school and never come back. That is not a class.
*: Small explanation for people who went to college in the US or somewhere else with a similar system: In here, university is usually 6 years (which is roughly BS + Ms for scientific disciplines, and usually ends with a thesis) of classes that are directly related to your career. For CS you have math, some intro to physics and chemistry, CS-specific classes and nothing more. In my understanding, degrees in the US are a lot more broad-spectrum, with about half of it actually teaching the specifics of your "major". CS is in the exact and natural science school and philosophy is in the humanities school, so classes are completely separate.