There's many flame wars around the internet about one setup being better than the other and what not. Let's face it, all depends on what you actually do on it right? One will be happy with a low end laptop to write his novel, others will praise their self built and highly over clocked gaming rigs, others will defend their video editing rigs or whatever. So what is your setup and what do you do with it?
I'll start with mine. So the main workstation is Apple Mac Pro (early 2009), 2x2.66 GHz Xeon, 10 GB RAM, 6 TB storage in total and Radeon 5770 graphics connected to Dell U3011 display.
I use it primarily for my work, which is mostly multi server system development (back end: video encoding / encryption, storage, business logic, front end: web stores, payments, reporting) which requires me to run many virtual machines all the time, a lot of terminals (or terminal tabs) open, text editors (primarily MacVim, secondarily BBedit) and obviously collaboration software and web browsers.
For that I really need a lot of CPU cores and fair amount of memory, storage and graphics card (now pretty low end, but it was decent when I upgraded it 2 years ago) are mostly used for my personal stuff as this computer also serves as my digital hub storing (and processing - final cutting and photoshopping) all the video and photos i take. For only work stuff (VMWare, Vim, email, Skype and browsers) I could be fine with some self built dual CPU rig running Linux, but OS X being basically an Unix with decent (can't say excellent or best any more as it's definitely not) GUI is really better for everything outside work.
I also keep a Windows 7 installed on a bootcamp partition to play games (I don't play on OS X as Mac ports plainly suck).
