You know, I honestly think it's 6 in one hand half a dozen in the other. I, as well, was between a brand new 2.0ghz or a refurbed MBP. Because I was at the store and the computer was being offered as a gift to me right then and there... I went with new. I didn't update the ram or the harddrive (in 4 years of having a 60gb iBook, I still have 15gbs left on it!), and the speed is amazing. I'm not sure what you'd be running on yours but let me give you a little example of what I have run simultaneously:
iTunes, GarageBand, 3 internet windows in Safari, 4 in mozilla, 6 different messenger conversations in 3 different messenger programs, Preview.
When iTunes and GarageBand were open together, I had a song playing in iTunes that I was playing the built-in piano along with in GarageBand.
Another time I ran:
Preview, Mail, 6 web pages open in 2 different browsers, 5 chat conversations in 3 different chat programs, a video chat, iTunes.
I'm on the 4th day of having this baby, and I haven't heard the processor or the fan once. So, if it's speed you're worried about, I wouldn't... especially if you're updating the ram and hdd anyway!
Now, when I asked a mac genius about refurbed vs. non at the store... here's what he said to me:
When you buy a new computer, you may or may not get some refurbed parts in it. When you buy a refurbed computer, you don't know what went wrong with it before... but again, some parts in it are going to be new and some are going to be refurbed and you won't know which. Neither, in his opinion, were more likely to break down on you, and shopping refurbed - especially if you're not a student and don't get the discount - is a good way to save some cash, and just as valuable because you can still get the extended warranty.
I hope this helps your decision-making process!