I really like Expression design. Having used it for a bit (including the ugly old pre-WPF interface), and most recently for Silverlight work, I've found some areas that could use improvement.

Do you also have a wishlist for Expression design? If so, post it over on Rob Relyea's blog. Here's mine (also posted there):

• When you use "copy xaml" have it copy hidden layers, but set their visibility to collapsed. This helps a lot when you are designing different states (hover/selected etc.)
• Nested layers
• Right-click support in the layers. I should be able to select, delete. etc. using context menus
• Warnings about things that will be lost (like bitmap effects going to silverlight), so keep designers honest :) (a preview in the target technology available as a discrete function prior to export could also handle this, and decouple the tool from a heavy dependency on each version of a target technology
• Integration with source safe and/or asset management tools with check-in/check-out
• Ability to create styles/brushes and store them in the same project. This is as simple as being able to keep the same gradient/brush as an in-project asset, usable across multiple items
• Ability to store same in an asset library accessible to the tool from any project
• Ability to tweak one item in a group (position etc.) without having to ungroup. Nested layers could eliminate the need for this
• (this is really for blend) : unify the UI across Blend and Design. The subtle differences can drive you crazy. For example, I like the gradient transform in blend (the arrow you can move around). However, the Appearance pane in Design is *much* more user friendly than the one in Blend.
• Tweaking on how selection works. I find my items deselected a lot when I am working on them. I'm sure it is stuff I do, but I don't run into this with other tools. I'll find that the fill I'm setting isn't attached to the object I thought I had selected a moment before.
• Similarly, some work needs to be done in the layers pallet to make it more obvious exactly what is selected and being worked on. For whatever reason, that just isn't gelling with me.