Kevin I'm not thinking of doing so, but the thought of loosing all my client data crossed my mind.
DL is hosted on Amazon servers (like many, many big name companies are), which are backed up constantly for redundancy in case there's any interruption of service.
That said, there are many download options so you can always periodically just download everything into excel files if you need to have a hard copy of your data. In Projects (Items & Work) there's a download option in the 'Reports' menu at the top. This will download the entire project- all items- into a csv (Excel) file that can be used in any way you'd like.