The come and go is scary, but even then unless you pay a lot of $ there is no gaurentee or SLA. Years ago a paid for the upgraded hotmail account and was backing up all my mail there until one day it was all gone with a note from the admins stating there was an issue.
Also if your backing up data online consider restore time. Sending the only changed file or two up there isn't that big of a deal but what if your computer is destroyed and you then have to restore, how long is it going to take to pull all that data back? It would take days just to get my pictures.
I've been tempted to set up another server at my parnets house. I have small low power 500MHz fanless via board that runs headless for my backup server, I could easily set up one there and have it pull data down from my home. My parents are in a dial up only area unless you want satalite so having a pull type system where my server at their house dials into the internet then connects to me and pulls data back could work. I keep my offiste backups there on dvd already