It turns out that Hostingsource has never been down unexpectedly in the 3 years that I've been using them. If they are planning on doing maintenance, they have always let me know. I have always been able to access my site, and my webmail.
Whenever I've needed help on anything, their support has always responded quickly, and have been able to help me with whatever the issue was. I would recommend them to anyone (and frequently do).