Personally, I can't use the optical media method as it's too repetitive and I end up forgetting or just not bothering.
Another problem that I would have with write-once media is that I sometimes go back and edit old photos. I could imagine things getting messy for me if I used CD/DVD back-up. Also, each disc doesn't store enough for my liking as I can easily fill an 8GB CF card in a day. At the last wedding I was at, I shot over 10GB in about 12-hours.
Perhaps, larger capacity optical media could be used for archiving...
Online backup is slow, but cheap. Mozy (part of EMC so they're pretty legit), for example, offer unlimited backup, but my upstream is 512kbps at best so this is proving to be a very slow process. So far, I've backed up 184GB using this method, but I've still got a lot more.
Ideally, I'd like a RAID array stored in my garage to back up my photos over a fast, secure, wireless network. Sounds a bit pricey, though!