Thomas, the current forms available in CRM Online are in many ways just a preview of the upcoming UI to be fully introduced in the next major version of Microsoft Dynamics CRM (Orion). Many of their limitations are due to the changes that will be applied to the navigation logic and menus in the next update, which means they are somewhat awkward to use in the current Polaris release that contains a mixture of ribbons, popup windows and process forms.
To get an understanding of where the user interface is eventually heading towards, please see the following blog post that contains information provided by the Dynamics CRM product's UX Manager on the design principles behind Polaris and Orion: niiranen.eu/.../the-next-dynamics-crm-user-experience-orion