Do you use Slideshare already?
If you answers this with "no", here is a list of reasons why you might like to consider sharing your presentations online:
1. Easy to share
Slideshare is to me the easiest way of having my content uploaded, in such a way that I can share it online (through LinkedIn, Twitter, Facebook, an internet forum, or an email contact).
2. Easy to embed
I also really like the way how it allows you to embed your presentations on any other website. I, for example, like to add some of the presentations that I've given on my blog through the easy embed option on Slideshare.
(And I precisely wrote "some presentations" - even though ideally I'd share everything, I still feel reluctant when it comes to sharing presentations of which the information hasn't been published in a paper yet).
I'm really surprised to see how many views my presentations actually get. My most viewed presentation, in fact. has drawn a similar amount of views as my most popular post here on the blog (that is - a little less than 2000). Here on the blog, my research-related posts typically attract less views than the content which is generally applicable to all PhD students. On Slideshare, however, my research seems to find an audience of its own.
4. Ability to find related content - and researchers
I've been browsing around on Slideshare several times to see which other presentations are seen as similar to mine. Mostly, I find more lecture-style presentations on my topic, and I haven't come across a researcher in my field who has his presentations up there. However, if I would come across a presentation from a researcher in my field, I wouldn't hesitate to get in touch with him/her - and maybe another valuable contact with whom I can enjoy sharing ideas could be added.