But (let me know if I am wrong about CrashPlan specifically) most of the "cloud" based storage I've used requires you to upload everything (you can't just send them a hard drive). I don't know about you, but around here both of our broadband providers only give 1mb/s upload. To even upload 1GB of storage means it would hog my entire upload bandwidth (rending my internet access virtually useless) for over 2 hours. Multiply that by 2048 (for 2TB) and you are dedicating 6months of your internet access to just uploading your library! At even $40 a month for internet, that's an investment of $240 in internet access fees just to get it uploaded (not to mention the additional $30 for crashplan).
Further, I bought 3TB drives on Black Friday for $100. I could buy two of them, (which is cheaper and faster than taking 6 months to upload), and I have the backups in my hands. If CrashPlan went belly up, I would have to find someone else and do it all over again yes/no?
To the point about not being able to hook up the drive in 10-20 years. That is a very serious problem. Years ago, we all backed everything up to tape. Problem is, tapes tended to use proprietary formats that now you can't even get the tape drives that your tape went into. With that said, SATA is not a proprietary format. Will it be around in 10-20 years? Probably not, but PATA which was around for well over a decade before SATA and is still possible to hook to your computer (I just had to buy a USB to PATA cable recently to make it work). My point being, is that if you use SATA drives, you should have plenty of time to move it to the "next big thing" before you have to worry about not being able to access your archives.
DVDR's have been proven to be unreliable (can't speak to blu-ray as I haven't looked into it). Even the best, have been found to disintegrate in less than 7 years even in the best of storage locations.
I always recommend archiving to hard drives and checking them at least once a year to make sure they do not need replaced.
Crashplan will send you a hard drive (for an additional fee) that you can copy your current files to and then send it back to them for them to add to your backup set. Then, you will just have to start backing up the new files you add. If you aren't in a hurry to backup, you can schedule the backups only to occur when you specify them, such as overnight. Also, I wouldn't factor in the cost of your Internet service into the overall cost simply because you would be paying for it anyway.