I've been watching ebay for carbon bikes, and they have poor resale value. I just saw a $2500 2004 frame go by for 1300. And even though I'm looking at buying the lower priced frame from the same company (Kuota) I couldn't bring myself to bid on it. It was my size and it was somewhat local so I could have checked it out before committing.
I've been checking eBay for any cheap old frames that might show up and noticed that carbon frames seem to go for pretty cheap. I'm not looking for a carbon frame, but it got me thinking about whether I would buy one used on eBay. I know that the fear of carbon breaking is irrational, but for some reason it's still there.
Then I got to thinking and it seemed kind of funny how some people still don't trust a carbon frame, but carbon forks are everywhere. I wouldn't really worry about buying a used fork. I guess I wasn't thinking about how rational it would be to upgrade a carbon fork, just that it wouldn't scare me to buy one used if it was out there and I needed one.
Would you buy a used carbon seatpost or used carbon wheels? That's a lot of money to spend for something you can't sell when you're done with it.