I use Skype both personally and professionally. I moved to Florida about a year ago, and my youngest son stayed in Iowa to go to college. We have a weekly Skype date which is nice because I actually get to see his face as we talk. Professionally I use it to Skype remote workers into meetings so all can participate.
I have used Skype also, both personally and professionally. I think it's a great resource to use for a guest speaker. More and more students have a 504 plan, so this could potentially be used to help them participate in class discussions.