Etiquette on LinkedIn is tricky. LinkedIn is for people to network and advance their careers, not share what they ate for breakfast (Twitter) or their vacation pics (Facebook).
Here are some tips:
• Although it’s tempting to kill two birds with one keystroke, don’t link your LinkedIn status updates to your Feedback and Twitter updates. Each medium is different (see above), and should be treated accordingly.
• If you want to connect with someone, you should have worked with that person at some point. I’m not a fan of “pre-friending,” or friending someone in the hope of subsequently working together. Alternatively, asking a contact for an introduction is perfectly acceptable, common, and beneficial.
• If you want a reference, you’re going to have to ask for it; few people volunteer them. When requesting a reference, I’d advise people to change LinkedIn’s default message to something more personal. Also, it can be helpful to send a separate e-mail letting the recipient know what you’re requesting.