Stick with a reputable seller and you should be fine... "Manufacturer Refurbished" is better than "Seller Refurbished", and as already stated, look for some type of warranty. In the case of a laptop, if it's still working fine after 90 days, you have a good chance that it will go the distance--the majority of problems will show up right away. I've seen people purchase extended warranties and never use them...and of course I've seen things fail right after the warranty expires--so there is always some risk.
Personally, I have purchased one refurb laptop (Acer), and it appeared to be new. It was a gift for a family member, and it turned out great (still running strong after two years). I've also purchased refurb desktops in the past, as I needed "servers" for a lab, and again, had no problems.
Just the other day I saw a comment on a refurb item, and the happy purchaser stated that he actually prefers to buy refurbished, asking rhetorically; "the problems have been fixed, right?"