Yes, I experienced the same thing. I have been hosting 3 Wordpress sites on Dreamhost since April 2011. Starting in August 2011, the sites started going down so I emailed the support desk on Dreamhost and they tell me I have to upgrade to the VPS service. I did not change anything on the sites.
This is their way of getting more money from their customers who thought they were getting $9.95 per month (bait and switch trick).
For over a month I tried to lower the amount of memory that one of my sites was using. I have dozens of emails with Dreamhost support (who are very responsive by the way) telling me to turn off this and that plugin. I removed all the plugins they told me were memory hogs to no avail. The memory being consumed was still too high.
But the thing that really pissed me off was the email from support which told me that they were still working out a way for Dreamhost customers to figure out exactly how much memory they need but in the meantime, Dreamhost has a very aggressive script that just kills your website. Here is a snippet of the email they sent me:
"We are working on a few solutions to correct the issues we're seeing. The biggest issue right now is that customers do not have a way to see if they are hitting their RAM limits on the VPS. The reason why it doesn't
show in the panel usage charts is because the memory request is denied. For example, if you have 300MB limit set, and you're using 280MB, and a request comes in for 50MB, it'll just get denied. That's why the graph will never show you over your RAM limit. This is the reason why we are working on a notification system which will inform customers about hitting their RAM limits and increase it temporarily for one week for customers to either find the cause of the high RAM usage or increase their RAM. We are also working on a system for us to be able to find which VPS servers are causing the most issues on the VPS and tracking them. Right now when oom is triggered it's hard to track down what VPS is causing it. We need to have a better monitoring system on our end which will help narrow down problem users and then either move them off to another host machine or disable them if they are not willing to cooperate with checking their code for problems that cause high usage."
I have no problem if Dreamhost decides to change its policies and implement this but they need to warn customers IN ADVANCE or wait until this procedure is in place. In essence, what Dreamhost is doing is sneakily increasing the monthly fee that you pay them.
So I've decided to leave Dreamhost because their total lack of concern for the uptime of their customers' websites is not acceptable to me.