Bad teaching is one of my pet peeves, but I go back and forth on PowerPoint. I think its egregious abuse most of its users shouldn't necessarily bring a cloud on the whole program -- sometimes it is used effectively. Still most people are not using it correctly, in a way that facilitates good teaching rather than is a crutch for bad teaching.
Chad Orzel from Uncertain Principles has an excellent guide to using PowerPoint for good rather than evil:
2) Limit Your Material. I tend to view one slide per minute as an absolute upper bound on any given talk, and I rarely reach that. The most recent public lecture I've given ran twenty slides for a 50-minute talk, and I rarely have more than 15 slides for a one-hour class. The colloquium talk on my current research runs about 26 slides, and also tends to run a little long.
I've seen more speakers than I care to mention show up with 75 slides for a 60-minute talk, and those talks never end well.
3) Equations Are Death. Yes, physics is a mathematical science. It doesn't mean that people want to look at slide after slide of nothing but equations. There are few experiences as soul-crushing as sitting in a dark room watching somebody do algebra.
It's almost impossible to completely avoid equations, but make sure you limit it to only the absolute essentials, and do everything possible to simplify them. If your equation has a big clump of fundamental constants out front, consider grouping them together into a single overall constant, to redue the visual clutter.
4) Text Is Death. Specifically, don't put complete sentences on your slides. Most people can read faster than you can talk, and if you present them with a dense slide of text, they'll focus on reading it, and tune you out. You want them to be listening to you, not reading your slides, so keep the text to a minimum. You need enough that the slide will make sense to somebody who gets distracted for a minute, and misses some of the talk, but you're not writing a novel, you're giving a talk.
Read the whole thing.
The best advice here is probably: "You want them to be listening to you, not reading your slides," but I don't believe that means you should stay away from complete sentences, which leaves incomplete sentences, and potentially incomplete thoughts. I prefer Edward Tufte's recommendations:
http://www.edwardtufte.com/tufte/books_pp
http://www.edwardtufte.com/bboard/q-and-a-fetch-msg?msg_id=0001yB&topic…
It's easy for PPT to become a tool for evil. Until recently, I was largely opposed to its use for teaching. However, that has changed since I coupled PPT with Mimioboard technology. The ability to markup PPT slides in realtime in front of my students has produced the first significant change in my teaching style in 10 years. Great stuff.