Now, I had worked on a project a couple of years ago where we suffered this a lot. I think that one was BizTalk Server 2006 R1. After having done some stints with BizTalk 209 / VS 2008 it came as a nasty surprise to be getting this issue again.
As you might expect, I decided to search to see who else had had the same issue. I got a couple of relevant hits. This one, http://continuouslyintegrating.blogspot.com/2008/01/orchestration-designer-crashes-visual.html, was interesting as it implied that there was something in your profile that was causing the issue. I didn't really want to have to rebuild a profile in the middle of a critical phase in the project so I kept searching.
I then came across this one, http://www.sabratech.co.uk/blogs/yossidahan/labels/visual%20studio.html, and more things to try. The thing that seemed to be intuitively right was that the size of the orchestration might be an issue. I had only started experiencing issues once I started to work on huge orchestrations. Before that there had been no problem. When working on modest orchestrations there was no problem.
I therefore took the suggestion that had the least amount of pain, to decrease the colour depth in my display settings from 32-bit down to 16-bit. I was hoping that this was going to do the trick. I then started working on the offending orchestrations and I could at least get started, but I did experience further crashes.
I then thought of a further step I might take, and it seemed to follow on from reducing the graphics load. I zoomed out. Never had another crash after that!
I think part of the problem is that the orchestration designer renders the orchestration as an image, or rather as a series of overlapping images. Then, depending on where you scroll to, a certain portion of the image is displayed. Therefore, no matter how small your viewing area in the designer the orchestration designer is still rendering a pretty big image. However, if you scroll out you reduce the overall size f the image that needs to be rendered. And, as mentioned, if you decrease the colour depth you reduce the size of it still further.
Huge orchestrations, from a design point of view, are bad. Huge orchestrations, from the Visual Studio Orchestration Designer point of view, are bad. If you must have them (as in my case where I was handed them and had to make them work), reducing the graphics load on your machine is a quick way to prevent Visual Studio from crashing under the load.