OK so what happens in the actual release? We do a rolling release in which the script goes to the router and re-routes traffic to the other servers (basically takes a server off line). The script then deploys to the server, brings it up verifies it and then turns traffic back onto the server.
A couple of principals that we live by are that are back end applications are REST services, we don't do Java, or RoR, or .NET apps, we do REST middleware with a language, ours is Java but it could be any. This is a huge distinction because it means that we don't do JSP, JSF or any of the other server side frameworks. This makes our server side very easy to mange.
Also we don't use session. All of our services are stateless. Which means we can drop in a new service or section of an overburdened service to dedicated hardware with out all the implications of session. This allows us to handle traffic without having to deal with the context of that traffic. If we experience heavy load on the profile service we can drop in 4 new boxes with the profile service on it and route request to those boxes. We don't have constraints that require them to go back to the same box they have a session on or complex session management infrastructure to ensure context is there for a user when a request comes into that box. Basically any request, at any time, can be services by any box, with no need for external information from outside the request. It is completely stateless.
On the database side all developers write delta scripts that take the database from A to B. We also take the cumulative patch set apply them together and generate a clean version x.x DB script that is more efficient. when a release goes out the scripts are run against a DB that is taken off line and that DB is brought up in unison with the app server that is at release x.x.
As well with the DB, we have a script that exports fairly static information that is in the DB out to static json files on the web server.
Finally, we don't template html files on the server, we write JavaScript UI apps that pull data from the json files and the REST services, we use a CMS to do templating and the CMS exports static HTML to the web server. Dynamic info is overlaid on the client side via JavaScript. This makes the web assets deployments drop dead simple.