In my application I have a large number of forms. The forms consist of one main content block and a number of side content blocks. The content of these side content blocks depends on the form. However, some content (like a template grid with certain information) appears on multiple (but not all) forms. Is it possible to reuse these content blocks, defining its content just once (and thus maintaining the design just once)?
You can place the content that appears on multiple forms in the layout container.
Use snippets as Roeland suggests for blocks that appear on multiple layouts.
A combination of layouts and snippets gives you maximum flexibility and minimal maintenance.