I've got similar issues with my DNS host. Their Europe-based name servers have been getting hit hard by DDoS attacks and last week they were down for nearly three days. They don't respond to support requests and ignore their Twitter feed except to post updates that don't really say anything. I finally decided to start switching to a new DNS host and so far have been very happy even though it costs more.
I've found that guarantees like x% uptime are meaningless because it doesn't actually guarantee any uptime, just that you'll get some kind of refund when they're down for too long.
I hope your sites come back up soon.
If only there was a decent host provider. Must we do it ourselves?
Unfortunately I think the answer to that is yes. All my sites are on my own dedicated servers and so long as DNS is good to go the sites are up 100% of the time.