Have you tried Author Stream.com ? This site is a more professional site for uploading power point presentations than Slideshare.net. Furthermore, it offers you the chance to:
present live
upload to youtube
share your powerpoints
embed in blogs and websites
send free greeting cards and more

It seems to me that this site would be extra useful for large libraries. Here are a few examples of what could be done:
teach a live class using your powerpoints and invite a large group of people or certain classes at an academic library to watch
promote the library by uploading content and including it in your library web page
run a promotional campaign
what other ideas do you have?