It had to be done. My computer felt slow despite the fact that my desktop computer was an overpowered Mac Pro from 2 years ago stuffed with too many cores and too much RAM for the work I do on it. My MacBook Air, iPad and even iPhone felt so much more fluid for day-to-day use than the Mac Pro despite all of them having much less computational horsepower. Sure the Mac Pro was a beast when I was encoding video or building a Keynote presentation full of large assets, but booting, launching apps or even switching between tasks was noticeably slower than even my iPhone.
The Mac Pro was held back by a mechanical hard drive. Every other device I use had an SSD, and I was spoiled. Only the Mac Pro had to wait for a little part to move and search across a spinning disk to find information. I'd held out though for capacity. My data set won't fit on any contemporary SSD. My solution has been to keep my working data on Dropbox, and use my Mac Pro for archival storage. I have a pretty extensive Backup/replication strategy (Most data replicated across two computers and Dropbox, both computers backing up to Time Machine, both computers backing up to Crashplan).
Then Apple released new iMacs and several points caught my eye. First was quad-core i7 option at 3.4 GHz. The next was a 2GB Radeon 6970M. Finally was the option to get a 256 GB SSD with a 2 TB HD. I decided to get the iMac and move my home directory to the HD while keeping the OS and applications on the SSD. Then to boost speed a little more, I symlinked some directories back to the SSD from my home directory (~/Application Support, ~/Caches, etc.).
The end result is the most responsive computing device I've ever used. Day-to-day tasks are fast and responsive, but there is still ample CPU for more demanding tasks when needed. The speed, capacity and massive display make my other devices seem like compromises necessary for mobility–and I'm finally using my Macs more than my iPad again.