My colleague Mike has completed a series of posts on hosting the Workflow Designer. Important? Yepo - as right now the documentation in this area is somewhat sparse. I posted on this back in May and have not seen that much stuff come through since then.
I did come across a useful post on hosting rules correctly but - that and Mikes is pretty much it. Shame - as it has become an important piece for a couple of our UK early adopters and I would love some more info in this area. Fingers Xd for final documentation.
Nearly forgot - there is also an example of hosting the designer in ASP.NET using ATLAS - nice (and also without ATLAS)
Interestingly a number of our ISV early adopters who had planned to host the designer have since realised they would better serve their end users by creating their own designers or wizards generating XOML.