Only connect to the people I know in RL. Try to keep in touch once in a while, esp. with the ones who aren't close/interesting enough to follow in LJ, FB etc. Look for potential partners/insiders when see people changing jobs. From time to time ask for a reference on people applying to our company.

Do not use for discussion boards, socializing etc.

Also, people who're coming from outside usually google me; some report my public profile lets them prepare for the interview better. I would maintain it even just for that purpose.