Given the harcore users around here, I'm surprised no one has brought up virtualization.
I'm running the aforementioned MacMini. It's fine for surfing, iPhoto, light GarageBand, etc.
But run up a virtual machine? Even with memory to spare, a single virtual machine has both cores maxed out without even attempting anything intensive.
I'm using it for casual reasons, but there was a time I was developing applications for multiple target OS's. Being able to run those OS's concurrently and verify the cross-compiling effects of various methodologies would have saved me days, if not weeks.
I'm sure I could do it (albeit very slowly) on my current machine. That said, I'm also sure I could max out an 8-core machine with little effort if I so desired.
The shortening of my story is that I am looking for a Mac Pro. Probably a previous-gen 4x2.66 model, but still. I have clearly determined that it is necessary for the type of casual computing I do. I'm not using it for my professional work, and I'm not doing video rendering.
But it's still necessary.
Certainly I can't be alone in this?