Do I have some weird setting that is making this happen? I only want to change the text of a message box (and no other assemblies depend on that one) yet VS rebuilds all of my
You can exclude projects from your general build through the build menu..
Build → Configuration Manager → Uncheck projects that you don't want to always build.
This can massively speed up build time by only building projects that absolutely need to be built every time.
Note though you will have to build the projects that you've unselected independently (right click->Build on the project etc) if they need to be rebuilt.
You can also setup alternate build configurations so you can mix and match what will build when.