Maybe it is a problem with my host server, and maybe this isn't something that can be handled within the WordPress "engine", but I'm almost always timing out (returns a page 404 not found) when I hit the save or publish on most of my long posts, especially those with html in them. Long posts specifically, not short ones. I've had the same problem with 1.2 and 1.5.
When the SAVE or PUBLISH is clicked, I believe WordPress goes through and cleans things up, so maybe this is where the time out to a 404 occurs. Ideas?