As long as the back-end is a single machine and not a load-balanced farm *and* the number of saved files is relatively small, this will work fine. A shared filesystems across a farm presents it's own set of challenges as does a large number of files in one directory. For load-balanced farms, I would pin the service to one machine and if the number of files is expected to be greater than 10K, I would use some type of directory partitioning scheme to keep the number of files in a directory low (for those times when you need to manually read the dir).
