This is a topic that has seen some discussion here, but it tends to be fairly specific (e.g. "should I buy this model of Mac Pro?") and my question is more general. I'm about to purchase a new computer to replace my late 2009 27" iMac, and am probably going to get a 15" rMBP (the higher end model), as this would also serve to replace my aging 11" Macbook Air. I'm pretty confident about this purchase, but it is a little on the pricy side, and the size of the 15" rMBP makes me wish there was a way I could just buy a desktop and a laptop separately. Only, I don't really favor the new iMacs over the new rMBP, so I wrote them off early in the shopping process. But I've read some stuff about used Mac Pros that seem to indicate that they're workhorse desktop computers, even years after they were released. I've snooped around on eBay a little bit and found that a lot of them have 16GB+ of RAM, multiple quad-core CPUs, multiple GPUs, enormous HDDs, and extensive capacity for upgrading. They also often hover in the $1200 range, which would free up some cash for me to supplement it with a new Macbook Air (far more portable than the 15" rMBP) for about the same amount as I'd spend on a 15" rMBP. My question is this: how viable are these older models? I'm not very informed about the myriad CPUs and GPUs out there, and on paper a lot of these computers still look like really solid performers. Am I wrong? How do they actually compare to current iMacs and the rMBP refresh?