Keep in mind that most of these services have a similar clause to this one. Check out the clause that is titled: "Changes to Service" and notice they can make any changes they want and they don't have to tell you about them. Also note later in their agreement the clause about "abuse". Since the term is not defined, it can mean anything. What usually happens with these types of services is that once you've used them for a few years and have a vast backup, they start playing games with the rates they charge. Also they often promise a large amount of space for backup, but if you actually use that space, they then invoke the "abuse" clause.
Keep in mind the reality of backing up photos. It is not unreasonable for many photographers to end up with several hundred GB of photos per year. Think about the huge hit to upload and store those files. And since most home ISP connection have a throttled Upload speed, you will find it takes a long time to upload the photos.
By the way, Carbonite actually has this statement on their site:
Notice that if you go beyond 40-50gb, then they will deny you service as an abuser. Now this is open to interpretation, but I am generally wary of all of these online backup systems. In any event, be sure to still do your own redundant backups. Also keep in mind that if one of these companies goes out of business, you may lose your data.
"The map is not the Territory"