I have been using Backblaze for around a month, and so far the experience is excellent. I have contacted technical support a couple of times (by email) and both times their response was within 24 hours and answered my question accurately. The only drawback I've noticed so far is that in order for backups to work in 'continuous' mode, you must leave your computer switched on for several hours after the latest file modifications in order for backblaze to backup the changes. As I tend to use the computer for a couple of hours at a time and hiberate it between uses, continuous backup wasn't working. However, if you select 'Backup only when I click on "Backup now"', the backup is done within 2 or 3 minutes and does backup all recent files. My current backup size is around 140GB, so an incremental backup taking 2 or 3 minutes is fine with me.I cannot comment on the numerous negative reviews, as my own experience is entirely positive so far.
