I've been having this same issue for a while now when trying to add or update posts. Some posts are ok, but certain content will seem to cause this ERR_EMPTY_RESPONSE error in Chrome. (In Firefox, the post will process for a while and then prompt to download post.php as if it isn't executed by there server, and in IE it will give a generic "Internet Explorer cannot display the webpage" error.
I've created a brand new installation of WordPress 3.0.1 on the same host with a different domain, and deleted every plugin, and this error happens there also. I've also run Check/Repair operations on all tables via PHPMyAdmin. My host has confirmed that they don't have any mod_security settings enabled that would prevent posts from being saved.