I have used Slideshare before when I was in grad school. I used it to present a PowerPoint presentation I had made. It worked out great! I have also used Slideboom, which is very similar to Slideshare. I really don't use Slideshare in the classroom unless there is a particular Slideshare I want to share with them. If I have made a PowerPoint to present to them, I just show the PowerPoint on my Promethean Board. I did find some great Slideshares to show my class. The library has really grown since the last time I used it, and it is easy to search.
I chose the Slideshare "Go West." It was pretty good, and it also gave me an idea to create one of my own on Western Expansion. I will show this to my class and see what they think. Maybe as a class we can create one of our own. Here it is: