I'm building a pretty stock standard N-tier ASP.NET MVC website, and I'm trying to think of all the little miscellaneous tasks that people often forget to do when building a site.
Off the top of my head things like:
What are the common things that people often forget?
People tend for forget to test the deployment and upgrade process.
Deploying the system to a production-like environment early on during the development process will uncover (often forgotten) external dependencies and configuration settings that need to be tweaked before production. Plus it will force the team to start thinking about the upgrade process and how to automate it.
Some examples of such tasks (from my own experience):
In my experience the main mistake or misunderstanding of people starting using MVC is that they confuse the C of MVC, the Controller, with the Business Logic and the M, Model with the Data Acess Layer or entity model.
I have given this answer a while ago and there are some comments about this confusion of the fact that MVC is only about UI controlling and modeling, it's surely not replacing other NON UI related layers... mvc3 and entity Framework