So far so good. We have been hosting several small sites with Rackspacecloud.com for a year or so now. There have been a few slow downs here and there. But they are usually short lived and resolved before our clients even notice.
If your sites don't require shell access or any sort of custom libraries compiled into your server, then try the rackspacecloud.com.
And we host our own servers as well. So that is saying something.