We have many customers using SpiderOak to backup production servers, using various Windows flavors, Mac OS X, and Linux. Anything that you could backup with tapes, external hard drives, etc. SpiderOak can handle. We also have a number of partner IT support companies who resell SpiderOak as a value added backup service for their business customers.
For Exchange, MS SQL, Oracle, and so on, SpiderOak works best by backing up periodic archives or database dump files. This is the most common way that backups from these systems are created, and this is the way probably 95% of administrators arrange for backups.
To be very clear: SpiderOak is not designed for backing up a "hot" copy of Exchange's data files, while Exchange is running and changing them. There are several rather expensive backup products specifically designed with Exchange plugins which can do this this. If that's what you need, then SpiderOak is definitely not the solution you want (or at least not the complete solution -- you could still use SpiderOak to archive the "hot" backups offsite as another product creates them).
SpiderOak is particularly well suited for storing a perpetual backup. For example, if you want to retain all previous versions of all files, all deleted items, and so on, SpiderOak's intensive de-duplication allows this to happen using minimal additional space. So for many business case scenarios, SpiderOak is ideal.