<p>I'm having real difficulties with XAML files in Silverlight since they get very big very fast when using Blend. It just becomes a wall of text after only a handful of controls are added and animated.</p>

<p>I'm hoping a better vesion of Blend will come out soon, so that our designers will never even have to see XAML. For now, though, that is not a solution - XAML still needs to be managed manually and it is a depressing task.</p>

<p>Has anyone found a solution to this? How do you keep your XAML files in order? How do you understand them when they get big?</p>

<p><strong>Edit</strong>: I am especially interested in Silverlight solutions, since the most obvious WPF solution - splitting things up into resource dictionaries - is not supported in Silverlight.</p>

It does require a little bit of work to maintain XAML files, but basically, what you need to do is split them up in resource files  (XAML Resource Dictionaries) using a scheme that makes sense to you.
For example we use a scheme where we have a folder structure like this:
Resources (contains XAML Files that represent the user controls and pages)
Stencils (XAML files with Shapes)
Styles ( XAML Files with styles)
Brushes ( ... )
Shared
Templates ( ... )
Your structure might vary but, separating all resources in different files really makes maintenance more easy in the long run.