I've used Carbonite for several years now and have been happy with it. For a single computer (not including attached storage), it's only $55/year, a wee bit less than $5/month (Carbonite also has plans for multiple computers and/or attached storage). It operates automatically in the background to avoid slowing your computer and encrypts your data before uploading it. It's the most up to date form of offsite backup one can have (and is probably more up to date than most local backups). The only downsides are it will only back up data, not the entire system, and recovery will be slow for large amounts of data.
That said, you shouldn't depend on any one form of backup. All media will eventually fail, be it tapes, optical disks, HDDs, SSDs, or the cloud. A bare minimum backup scheme should include one local backup and one offsite backup. With the exception of a plan like Carbonite, local backups are more likely to be up to date than off site backups. The downside of a local backup is the same disaster that causes loss of data in your computer, fire, flood, theft, etc. will also take out your local backup.
Of course, it is imperative that one keeps backups a up to date as possible. Also, the more backups one has in multiple locations, the less data one will be likely to lose. Multiple backups can be a bit costly and somewhat of a hassle but weigh that against the cost of the loss of your data, especially data that can't be recovered if lost.
While a bit extreme (as in anal?), my own backup scheme is to have three backup HDDs for every HDD in use. Two of those three are local backups. The third HDD is kept in a safe deposit box at my credit union. I use a paid version of Macrium Reflect for my back up images. Once a month, I do a full image on each backup drive, including the one in the safe deposit box (I swap drives to save trips to the credit union). During the month, I run an incremental backup on the two local HDDs after I add critical data to my computer I can't afford to lose (incrementals capture only data added since the last precious backup). I also have the aforementioned Carbonite account on my desktop computer (I don't keep critical data on my notebook). Having Carbonite reasonably ensures that any data that is missing from my other backups can still be recovered. Having the local and vault backups speeds the recovery of most of the lost data, with the rest being recovered from the slower Carbonite.