I'm going to be purchasing a used or refurbished Mac Pro sometime before the end of the year. The big kicker is that even the older Mac Pros are a big upgrade from my current mid '07 iMac. Also the upgradeability. I've seen a number of threads regarding processor upgrades, which seem fairly doable, if a bit complicated... But I was told in another thread that replacing the logic board in a mac is not "user serviceable". What is that supposed to mean? Not user serviceable as in most people don't do it because they just sell and upgrade to a new mac pro? Most don't do it because they don't want to deal with all of that jazz? Or is it more or less impossible to do? I don't have a huge budget, so I can't just blow $3500 on a new Mac Pro with 8 cores...and even if I get a used Mac Pro and upgrade, I'm more likely to have the money for upgrades... but I don't have the luxury of selling my computer and then buying a new one. I've replaced mother boards in plenty of PCs without a problem. What makes it so hard in the Mac Pro?