FWIW DreamHost's shared server hosting has more or less become useless to me due to 500 Server errors...
"But regardless, the problem is that you are using too much memory, and that your PHP processes are hitting our process watcher which is why it's showing the 500 error."
So basically the amount of storage space and bandwidth is immaterial. The problem, for me anyway, with DreamHost shared hosting and WordPress is the amount of memory allotted- and they don't give you that information- they won't tell me how much memory I'm using or how much I'm allowed.
This is a single WP install on a unique user with little to no traffic and Super Cache installed.
It's happening on all my WP sites but where I have more active plugins it's worse.
I was looking forward to WP 3 and multi-sites. I don't feel confident in even trying a multi-site install on DreamHost.
This only started happening around April 2010 when I was moved to a new server. I was previously happy at DH. Wouldn't recommend it to anyone running WP now.