Social Media Links (Placement/Usefullness)

I have decided to implement the most common social media plugins into my website design. These being FB, Twitter, Google & LinkedIN.

I am coming to you all because I am wondering what types of placement you have used and which scenarios you deem most useful. I own a web hosting company and have implemented the links on my homepage, plan pages, organization information pages, announcements and knowledge-base articles. I have added them to my header, but did think about placing them in the footer. Please check out placement (www.option9.com) and let me know what your thoughts are.

As well: For each page the plugins are on should I use my homepage as the href source or the current page url? Which would be better?

I'll start by answering your last question first. It should point to current page URL's. Having multiple pages getting tweeted is always a good signal for search engines.
The placement you can always test them out. Important thing is to show them clearly. Having them at the header is good for the home page. But for article maybe you should go for a sliding sidebar, so it is always visible to the user even if it's a long article. Again it's matter of testing out different options.