Marco Arment poses the question in this post.
It's a good question. After all, a loaded up iMac (especially with an SSD) is going to be very nearly as fast for doing a whole lot of things as a Mac Pro. One of his main reasons choosing a Mac Pro is disks.
At KAYAK, we give all engineers who choose Mac as their platform (ubuntu is the other popular choice) Mac Pros. The main reason is disks.
1. if a disk drive dies, we can swap in a new one in 2 minutes and have the programmer back to work within minutes; it might take hours in the case of a really bad failure. (This happened to me last week when BOTH drives in my RAID 1 config died. WTF.)
2. It's very easy and clean to have two RAID 1 pairs, one for OS/apps and the other for data. It's messy and expensive to have external enclosures for this kind of thing, and too many Mac apps just don't work with network shares of any kind. (Which is something that I find mystifying and annoying.)
At home, I'm on much more of a budget, and I don't have the worry of lost productivity. I have two iMacs at home, so worst case I'll have to go into the office vs. the family room to get something done. The disk drive thing is very annoying still; I wish Apple had a cleaner solution for external storage than 'buy random crappy enclosures and have cables everywhere.'
(Hint: an aluminum box with 4 drives and iSCSI: solve the cable problem and solves the iphoto-aperture-whatever-don't-work-on-network-shares problem)
