What I've probably longed most for in pages is the ability to have global variables. I thought this was impossible due to the lack of fields in a page.
It turns out it's quite simple. The reason I came up with trying this is Andre Guirards article on Using View Column Programmatic Names. In this article (recommended read!), he discusses the usage of FIELD in view columns/selection formulas to create temporary global variables.
To declare a variable as global, put FIELD in front of it.
For cross client (Notes/Web) pages, it seems that you have to put the global variable declarations in "Window Title". First declare your variables using FIELD, then add the code for the window title.
FIELD globalVariable := "I'm global!";
Using the variable in a computed text: