Microsoft Expression Blend 3 now lets you edit code without having to jump out to Visual Studio. You can of course still jump over to VS if you want, but how do you stay in Blend for quick'n'dirty code edits? Tools, Options, Project and the third checkbox is the key here! Make sure to unselect the Use Microsoft Visual Studio (Standard or higher) to create and edit event handler code, if available.
This will let you stay within Blend for those quick changes while still letting you keep your "designer train of thought!"
You can of course continue to use Visual Studio for those bigger code changes (and immediately try out your changes with debugging).
Now that you know how to stay in Blend for code editing, it's time to grab a coffee and get coding.