For the previous post about iFixit's laptop buying program, see here.
Their week-long wait estimate went by and for a late 2008, 13" aluminum MacBook (2.4 GHz, 2 GB RAM, 250 GB HD), iFixit offered $450. Which, in truth, isn't terrible. I would have put it at about $550 on the market, so iFixit's offer really is pretty decent. Could you get a bit more on Ebay? Perhaps. But that's assuming that someone would actually be in the market to buy a 4-year-old laptop, which is a pretty big assumption.
Just to give you some nice contrast, Gazelle — a typical "we buy and recycle your used computer" site — only offered about $275 for the MacBook. That's just a joke.
The Bottom Line
Could you possibly make some more money by selling it to a person rather than a service? Yes. Almost certainly. But that's assuming that you an actually make that sale. And that's a big hassle, especially if you go through services like Ebay.
iFixit's offer was actually pretty decent. Not sure what they'd give for slightly newer models, and again, they only do laptops, but if you're looking to avoid the hassle of selling an older laptop and are willing to take a slight hit on its value, iFixit looks to be the way to go.