I do like the idea of slideshare. Having been on courses and to conferences it is always useful to be able to revisit the presentations ( somehow there is always some point of the presentation one wishes to refer back to, however carefully one tries to write notes). In general I have found that those presenters who use slideshare for their presentations, have them up on slideshare quicker than those who rely on the conference/course organisers to put them on the website (possibly because slideshare enables one to put them up with restricted viewing and then change permissions later...making it easy to load them at the time of creation).
In the past I have only looked at presentations by people who have given courses I have been on - and I have found it interesting to see their other presentations. I can see that searching for topics; can provide a goldmine of information. I can also see that it could be a hit and miss affair (and one would need to check the quality of the presentations). I struggled to find presentations from Cambridge Libraries, but I suspect that was due to impatience on my part, and not taking sufficient time to refine my search - on the other hand, how many users would spend the time to do so if their first attempt fails?. Searching for other topics, I came across a variety of potentially useful presentations. I have an interest in Open Source software and its potential in libraries. However I have always found it hard to describe in detail - for those who are interested, I am including a slideshare presentation at the bottom of this post.
In a library setting I could see the benefit of putting some of the induction and library information on slideshare and embedding it in the library website enabling students to revisit the information as and when they need it (but probably waiting until after the tours before making it available!). I can also see its use for CPD (quality reservations allowing).
From the publishing point of view, when sharing it so publicly it could be harder to keep control over one's own work (I wonder how many people actually read the terms and conditions before publishing?)...although I suspect in the majority of cases this would not be a problem for the type of material that is published. On the flipside it could raise your profile, and if it became known that you create interesting presentations it could encourage course/conference organisers to use you.
In short I think it is a useful tool, which I currently use to access the slides of presentations I have attended. In the short term I will be looking at more of the presentations that are available...however it may be some time before I publish anything myself.