I would like to know if there is a way to simply turn of the WPF design surface in Visual Studio 2008. I would like to have the xaml editor, but not the design surface as it slows down the IDE, when I try to open a XAML file. For my workflow having only the source files for xaml would be a better fit as I am doing all visuals in Blend.
You should be able to right-click the .xaml file and select "Open With..." then select "Source Code (Text) Editor" (optionally clicking "Set as Default" to make it the default). This will open the file in the plain XML editor (you still get syntax highlighting and IntelliSense, too).
Tools->Text Editor->XAML->Miscellaneous uncheck Always open documents in full XAML view
The comment below informs of a catch when using this checkbox, that is it only affects files that have not been opened before. A solution from the link to the Microsoft Connect issue in the comment states that
If you really wish to reset the open/close behavior for all XAML files in your project, you can achieve this by closing Visual Studio, then locating the SUO file adjacent to your SLN file and deleting or renaming it, then re-opening Visual Studio. When you re-open your solution an new SUO will be created and all files will be treated as "new". Please note this will also remove any other solution-specific IDE behavior for your solution.