LinkedIn ettiquette?

If someone asks me to join their network on LinkedIn (the social networking site for professionals), but I don’t recognize their name and don’t think we’ve ever actually met, should I accept or not? I’m pretty good with faces and names, so if it doesn’t ring any bells, I really don’t know them. I guess it doesn’t hurt to add them to my network, but since it is a job-hunting site for professionals, it seems like I might not want to add them to my network if I don’t know who they are or how to vouch for them. One of the people I really have no idea how I might know them – the other (from her profile) used to work at my organization (but it must have been before I worked here, because I don’t recognize her name). Thoughts?