I got a refurbished white 2.0 GHz Macbook just last week. I seriously couldn't tell that this was a used computer at one point; it smelled like a new Macbook, had no cosmetic defects, came with all of the accessories, etc. What's the difference between this and a new one? It was in a brown box. That's all. Oh, the other difference: it came with an 80 GB hard drive right off the bat.
You seriously can't go wrong with a refurbished Mac at all. They also come with a standard one year warranty with a chance to buy a three year AppleCare warranty. They're also $200 cheaper, has a high chance of having free upgrades, etc. I also have heard of a guy that got a fully loaded refurbished black Macbook without paying a single extra penny.
i've never heard nothing but good things about refurbs, you might even get an unexpected upgrade. There have been several reports on these forums about these uprades, the most common being HDDs and RAM. But dont get your hopes up, its just by chance. I would recommend a refurb, unless you just have to have that shiny box.