Great idea for a thread!
My MacBook is a bit hot-rodded, here's the scoop.
In November 2011 I got a Black MacBook 3,1 circa late 2007. Model A1181, order number MB063LL/B. 2.2 ghz CPU, 2gb ram and 320 gb HDD.
It was in FINE condition, looked like someone had got it as a gift and never used it! Only issue was a piece of plastic strip ripped up a little in the lower right, where your right wrist goes, I understand now that this is a typical problem with these systems. That didn't bother me at all though as the rest of it was in like-new condition. I had always loved the Black MacBooks and had been looking for a good one for a while. I snagged this little baby from an ad on Craigslist for only $400, it was sold by a very small computer shop that two guys were just getting started.
First thing I did was sell my old laptop, a surprisingly not-so-bad Acer netbook, for $100, used that to buy a 4gb ram chip which I installed along with a 2gb chip I already had on hand (I'm a server admin so have lots of spare parts).
Second thing was to take out the hard drive, put in in an external USB enclosure to use for a backup disc. Then I took the 120GB SSD that was in my old Acer and put it in the MacBook and installed a fresh copy of Snow Leopard, which was almost immediately upgraded to Lion.
I was a pretty happy camper, it ran fast as any new laptop around and I loved being back on the Mac after years on PCs.
Happy I was, until summer 2012 and I wasn't able to upgrade to Mountain Lion. ( Confession here: on certain weeknights once or twice a month you can find me standing in front of a group of fellow geeks & nerds saying "Hi my names Steve, and I can't stop upgrading).
When Mavericks came out I lost control, went to eBay and got a motherboard from a mid-2009 MacBook. Spent about 3 hours following the excellent directions found on the iFixit website. No real difficulty just time consuming.
The only big issue was the screw posts for the mono were slightly different and I had to use some pliers to rip one plastic post out for the mono to fit in. One side effect is that 1 screw for the heatsink had nowhere to go, but there is enough pressure on it otherwise that it really doesn't need it. ( I monitor the temp with Bjango tools and it runs nice and cool even under load.)
So now I have a Black MacBook with a mono from a white mid-2009 macbook 5,2.
The CPU is now 2.13 Ghz, but I can't feel any difference. The system bus is faster at 1066mhz and I had to get new memory but only 4Gb now. Still have the same 120GB SSD drive.
Now I have Mavericks running and life is good!