I use LinkedIn for many reasons: Networking, Education, Discussions and more.
I host two key groups on LinkedIn:
Shopability Matters: Focused on online store usability and conversions. This is an open group (anyone can join), but is followed closely to weed out spamming and overuse of self-promotion links. The purpose of the group is to share information and gain more insight on the topic of shopability.
webOS Enthusiasts: If you use a Palm webOS device (Pre, Pre Plus, Pixi, Pixi Plus), then this is the group for you. We discuss apps, features, loves and hates, and everything webOS. Key news is also frequently posted.