How could I cache an entire page except a bit at the top which says something along the lines of "Welcome back, Matt! | Log Out" if the user is logged in and so-on?
I'm using ASP.NET MVC 2.
What you are trying to achieve is called donut-caching or cache substitution. As of ASP.NET MVC 2 there is no built in helper to support this scenario. As much as I know it was a planned feature in MVC v.1 but it was dropped somewhere in the way to the release. For more info check this links http://haacked.com/archive/2008/11/05/donut-caching-in-asp.net-mvc.aspx, Is Donut Caching working properly with ASP.NET MVC?. VaryByParam option that is mentioned by Oleg here is not a good idea in your case. If you have VaryByParam a different version of the page will be put in the cache for every different value of the parameter (in your case for every user-name). Personally I would think of caching the data, not the whole output of the page.