How do I prevent document preview over slow connections? Once in a while I have to work over a 3G network, which is reasonable, until I mount a file system on the other side of the world.

When that happens OSX tries to show me "previews" of every single document in the finder, an operation which takes forever because it usually tries to download the entire document in order to generate the preview. After spending hours downloading a 5 MB file, it often decides, "oh gosh, I don't know how to show thumbnails of Word files. I'll just show you a Word icon." In the meantime Finder is in bouncing-ball-hell for hours.

Is there a way to prevent this specifically for network shares when I'm connected over a slow connection? Or, failing that, just prevent document preview for all network documents?
You can disable Icon preview in the view settings.
For example: right click the desktop and select "Show view option" and then uncheck the last box.