A new test version with a likely fix for this issue will be ready very soon.
An issue was identified in the drag & drop code which would only have affected 64-bit versions. Of course, it's possible there was more than one issue, so your help testing will be very useful.
If you want to help test it and confirm whether or not the problem is solved for you, please contact GPSoftware via their support page (linked in my signature) to receive details of the test version.
A new version of Opus is out which should fix this. See the Announcements forum or the News Blog Page for full details.
I take it "no news is good news" and all the x64 drag & drop crash problems are fixed for everybody using 9.1.0.1 now?
Hey nudel,
I downloaded and installed last Friday and have not experienced any crashes. However I have been quite busy so have not had much time to test. Hope to do some testing this evening GMT.
I've done some pretty heavy file operations with the latest version, 9.1.0.1, under Vista x64 the last days, and it has been rock solid so far! So I can just say thumbs up and great work with this update! 
I too have not had this issue since installing the 9.1.0.1 update. Thanks a bunch GPSoftware! You rule!
Thank god that's been put to rest - so far so good. Will report if that changes! Thanks for the update.