Depends on your definition of long term.... I have still running computers older than some online backup providers.
Online backup is (IMHO) a useful tool for a second backup. It is not a replacement for an onsite hard drive copy or an offsite hard drive copy.
A few of the vendors support a seeded backup, but not all. Seeded backup is where they send you an encrypted hard drive, you make an initial backup to that then ship it back and they load it into your account. From there you backup to that initial seed. This means if you have 200GB of images to backup you dont have to wait weeks or months to upload that 200GB. This is really the only way to start backing up a large amount of data, but it costs some money.
Another thing to consider, if you go out and shoot 20GB worth of keepers, how long will it take you to backup? Depends on your internet connection. If you lose all your data, how long to restore? Again, some will ship you a hard drive... For $$$.
Myself, I have my NAS that stores all my images, DB, previews, and all other files on RAID6 arrays. Important stuff is regularly mirrored to hard drives that are stored off site. I dont yet bother with a serious online backup strategy, the cost is too great to backup all my important files and all my images. And I dont have the fastest internet so it would take forever to backup. I tried a few out and IMHO one of the better ones is Crashplan.


