My sites were down for just over an hour yesterday. They've all gone down again at the same time today, it's been 20 minutes so far. Dreamhost say this:
"Sorry about that! This is due to a recurring issue we're experience with a few Apache services. Our admins are aware of it and continuing to look into it so it is permanently fixed.
It looks like your Apache service was restarted about an hour after you wrote in, and everything is back up and running normally again.
I do apologize for the inconvenience and thank you for your patience as we work to resolve this for good!"
I've been pretty patient with DH over the years; they've had their ups and downs, but they offer a good service for the price. But if this carries on much longer my patience will run out. It's been happening for a couple of weeks or more now.