My system is too frigging big for optical drives, unless I cough up for a Blu-Ray burner. Besides, you have to burn new disks for each backup. The erasable ones have not given me great service.

Hard drives are fastest. I usually manually back up my day's work on my nearest backup computer, just a chair-roll away. When I get around to it, I run backups on my laptop. This covers the most likely disaster - a localized drive failure.

For worst case, like my whole house burning down, I have Carbonite for offsite backup, and it's automatic. I never have to think about it. The bitch with Carbonite is that it's great for recovering a few files quickly, but if you have to re-create an entire hard drive's worth of data, set aside about a week. Also, it can't do C-drive disk images.