In answer of your question in the panel.dreamhost.com under mysql in goodies you can get reports of you current monthly conuries (sic) much like you can get bandwidth and disk usage reports.
When I first started to setups forums, and generate dynamic web content I 'worried' about the impact on server load on the 'shared' servers I was hosted on.
What I really like about the dreamhost conuries (sic) is that I can measure my usage and realise that I had nothing to worry about at all.
In my opinion a good host is one that allows you to regulate yourself, and for that you need usage information.
One of the reasons why I signed up with dreamhost except for the newsletters, is that they were the only host I could find with clear guidelines on mysql usage and ways to monitor it.
I signed up a week ago with the belief that there was a cap on mysql usage per month, I was unhappy with that the last two hosts I have been with have had terrible reliability on their mysql access from over loading.
As it turns out there are no defined limits, but I like the idea that very heavy users can be informed by Dreamhost to have a look at their mysql access and try to optimise it rather than causing other users on the server suffer.