I use a V3 with a custom UI packaged (I don't remember the source of package).
I don't know why (Custom UI ? another plugin installed ?), but when I save a .3dm file, a .jpg looking like a screenshot (or snapshot) is generated too.
So I have 2 files a .3dm and .jpg in the same directory.
For my usage, this is a pretty good solution to preview.
Someone know the source of this feature ?