Depends on who refurbished it, usually when it's refurbished by the manufacturer they do a good job. Never bought one though, that's just some experience harvested from various stories and friends.
Depends on how old it is and what parts the refurber could get. I have an old IBM NetVista system that got stripped of parts, after replacing said parts i found that the mobo had died. turn on = no post or beeps.
Usually they come with some sort of warranty though.
You get it cheaper. Personally refurb is no more a gamble then buying something off a guy on ebay/this forum. That basically all a refurb is. Someone bought the item and returned it within 30 days for what ever reason. Most the time if there was a issue they fix it THEN sell it so the odds of having the same problem again are very minimal.
I have had very little issues with refurbs and the money saved was worth it.