For me, I use LinkedIn to find people and then as a communications tool associated with this blog. However, I'm seeing more and more people use it as their everyday email communications tool. Personally, I like using my "normal" tools of Exchange for my personal emails and Gmail (not my favorite) for my work email.
A few years ago LinkedIn had a feature where you could download a Vcard for the person who sent you an invitation. That Vcard could then be sucked into your contact database in Exchange. The company eliminated that feature because I think they want people to use LinkedIn to communicate. Certainly not a Burger King "Have it your way" solution to customer service.
Maybe I'm showing my age with my preference, but using Exchange gives me much more flexibility in how I use my contacts. My LinkedIn profile has 2,316 contacts, but in my personal contact database I have 10,385.
What are your preferences for using LinkedIn, and which system do you prefer for communicating via email?