I have been using online backup for many years. I won’t call myself an expert, experienced maybe, but I have tried almost all online backup and sync and share services. My biggest concern is still the longevity and trustworthiness of the provider.
My biggest disappointment is definitely Streamload. Streamload was a great service, they provided unlimited storage, had a client up-loader, supported FTP access, and had a great web frontend. And this was in 2005, long before many other online storage providers existed, and nobody else offered unlimited storage. The concept was great, take any of your online files, and present them in a web friendly way, e.g. play your backed up music collection from your browser, watch your backed up movies from your browser.
Unfortunately things did not go so well. Over time Streamload became MediaMax became TheLinkUp, none survived, but a spinoff Nirvanix did. Unlimited storage became limited storage, FTP access was revoked, free accounts became paid only accounts or loose your data. The final death-blow came when user account data was “accidentally” deleted, about the same time as MediaMax filed for bankruptcy, leaving thousands of angry users with no access to their data. Needless to say I was less than happy, but no point in reliving the past, you can read about the saga here, here, here, here, and here.
By the time MediaMax died, I had close to 1.3TB of data online. Yes, that’s a lot, but it was so easy to add without concern for size (MediaMax no longer offered unlimited storage, but unlimited accounts were grandfathered in), whenever I made a local backup, I just uploaded it online, and never deleted old backups.
My point is, a backup is only as good as its ability to restore, and what good is your backup, if you can’t access your data?