Since the introduction of 1TB drives, I've always used raid, and lot of backups. I use individual 1TB drives as "tapes" for backup, and I have offsite backups as well to my online server, though those only cover the most critical data such as code as my internet upload sucks too much to do big backups. Takes about a day to upload 1GB. Raid 5 is nice because you can expand it on the fly without any downtime, if you use Linux MD raid. Though I think my next setup I will probably go raid 6.
For my OS I could see myself use a SSD as they have come to a point where they are affordable now, if mass storage is not what you need. But for data, always spindle. It's crazy how cheap they are... though you get what you pay for, today's spindle drives are much less reliable than they were 10 years ago.