I have a VPS (virtual private server) which is hosting quite a few services (postfix, proxy, apache and mysql etc), and it only had 256MB of RAM. Running WordPress especially the admin pages were nightmares, I guess the box ran out of RAM and constantly using SWAP, and you know the VPS IO usually pretty slow… I couldn’t handle it anymore and upgrade my VPS to 512MB, and woola! WordPress is running like a charm!