I personally like AutoCAD, BUT, that is because I have modified/personalized it tremendously. As far as AutoCAD electrical package (available as an add on to Architectural Desktop) I found the package to expensive for no benefits and those I have checked with have given it mixed reviews at best.
I would recommend looking at your needs. Are you heavily into design or is this just showing a few devices in a residence? Then talk to others doing the similar work.
The only things I would personaly recommend in design software is that it work, be easy to learn, and be customizable (if you have to do things this sort of thing often), so with a little training you can make it work like you think it ought to. You may also consider do you need drawing compatibility with something else.
I am really looking for some software that I can use to add slides to my seminars
Joe, I would highly recommend the use of a SmartBoard for any kind of technical presentation. I've used one for over five years, and would be lost without it now.
It is an interactive whiteboard that connects to your desktop or laptop computer, and becomes, in effect, like a second monitor. It can be wall mounted or on a portable stand, and is used with an LCD projector. The screen is touch-sensitive, which permits you to operate any application that is on the computer by touching the screen with your finger or any pointer. That includes the internet (your web browser).
You can also mark over, or highlight, your presentation slides, draw diagrams, make notations, and either erase or save the mark-ups.
Use the bundled software, SmartNotebook to create your presentation, or use the software of your choice.
You might want to also consider using Flash animations. They can be used with lcd projectors, etc., Animated could show current flow, change of state, even fires and explosions, with sychronized sound. You can import diagrams, photos, etc. You can pause, and even step through in slo-mo, and frame by frame. Makes for a much better show than Powerpoint. Learning the animation program takes some time, but the end product might be worth it.