One of the biggest problems with presentations is how people use charts and graphs. People have a tendency to put too much information on a screen or the information is so incomprehensible that no one knows what the presenter is trying to get across. Unfortunately what is lost is the fact that graphs and data can be an extremely powerful tool in your presentations -- if done correctly!
FlowingData, a blog that "explores how designers, statisticians, and computer scientists are using data to understand ourselves better - mainly through data visualization" is a site that you should check out if you want to see how effective data and graphs can be. The recently put together a Best of Flowing Data for January that you can check out as a starting point. It is a great blog and one that I check regularly because of the quirkiness of it, the effectiveness of the data and the great designs that go into the presentations.
Travis