This is a low cost option for the hosting company and they will usually offer some kind of data protection using a RAID system where data is copied across multiple disks. This is an entry level solution but one issue is that the server itself represents a single point of failure. It could be that the power supply fails which brings the server down for example.

Think of it like buying a pre-built computer versus building your own computer. When you buy a pre-built computer, it comes with everything already decided for you. You bring it home, plug it in, and turn it on and all the software has already been installed. On the other hand, when you build your own system you get to choose each piece of hardware, put it together, select your operating system, and install your own software. Building your own system takes more work, and you cannot simply turn it on and begin using it. But, in exchange for this additional effort, you get self-determination and control over your hardware and software. You can choose your favorite operating system and the apps you want to install, no longer beholden to the manufacturer’s one-size-fits-all selections. Similarly, with a Self-Managed VPS, you have to do some initial set-up and later management. Yet, you get to choose the software configuration you want to perfectly suit your operating specifications.
The golden rule for unmanaged VPS hosting is this: If you have a problem with your unmanaged VPS Account, it is your problem. If the problem is software related, resource related, performance related, need troubleshooting or configuration of software, or need general help understanding Unix or server applications, you are on your own and should not expect help from the web host.
All the features I've detailed to this point are valuable to the web hosting experience, but none matches the critical importance of site uptime. If your site is down, clients or customers will be unable to find you or access your products or services. It doesn't matter how great the features are, or how good it looks; if your site is down, it might as well not exist.

I have some sites hosted on a shared-hosting/cpanel environment and need to make a move up. I have some experience running my own server, but it is very basic (a local box to do live testing/file serv). My question is how difficult is it to run a VPS, should I buy a managed VPS (with stuff already installed), or unmanaged (blank box), and lastly if I go for unmanaged what steps should I take to keep my VPS secure? Edit: Also how difficult is it to backup files and databases? Can it be automated?
Your web projects come in all shapes and sizes. Shouldn't your VPS meet your needs more closely? Your project may need additional disk space or data transfer while maybe you don't need so much RAM. Don't get stuck paying for for resources you don't want or don't need from a one-size-fits-all VPS provider. We've got your covered! Design your perfect VPS at A2 Hosting! 
Our VPS Hosting plans all come with a high availability feature that essentially takes your VPS container, and empowers it with a cloud infrastructure. How does this work? We put a premium on your server's uptime, so we created an infrastructure of redundant hardware clusters that provides your partition with real-time redundancy. If for some reason there is an error on your server, there is another server in the cluster with that backup information ready to spin up. We utilize Virtuozzo, a virtualization solution built on top of OpenVZ.
Partitioning a single server to appear as multiple servers has been increasingly common on microcomputers since the launch of VMware ESX Server in 2001. The physical server typically runs a hypervisor which is tasked with creating, releasing, and managing the resources of "guest" operating systems, or virtual machines. These guest operating systems are allocated a share of resources of the physical server, typically in a manner in which the guest is not aware of any other physical resources save for those allocated to it by the hypervisor. As a VPS runs its own copy of its operating system, customers have superuser-level access to that operating system instance, and can install almost any software that runs on the OS; however, due to the number of virtualization clients typically running on a single machine, a VPS generally has limited processor time, RAM, and disk space.[2]