I run all of my services on a Dreamhost VPS instance. I have even upgraded to the newer VPS with 1GB of RAM. Yet, my WordPress instances have become stupid slow. Like 2-3 seconds to load a page slow.
I had chalked this up to the complexities of WordPress and the various plugins that I had installed. However, eventually I became so frustrated I tried disabling each all plugins and discovered that this had little effect.
After more poking around, I installed a query monitor plugin and discovered that my SQL queries were taking more time that I would have anticipated.
Frustrated, I installed the MySQL server on my local VPS, and then copied over my database. Viola! All of the slowness disappeared. I went from having 3 second load times to less than half second load times. The following is a chart from Google showing the load times each time it crawled my site. You can clearly see the date when I switched over.
The moral of this story is that the shared MySQL server that comes with a Dreamhost VPS account is absurdly slow. Stupidly so. Luckily, there is plenty of RAM on a VPS instance to run a MySQL instance.