Since a couple of days I'm facing the same problem, but I'm afraid it's not due to Safari.
Yesterday, I've seen it with AppFresh (which searches for updates for the applications i have installed). Some of the updates were downloaded but would not run ("The following disk image could not be opened. Not Recognized"). I suppose those files have not been entirely downloaded.
Today I tried to download Things with Firefox (
http://culturedcode.com/things/download/?e=3102). The file is 8.1MB, Firefox "terminates" the download as if it was successful when the file is below 1MB (I tried several times, got several sizes).
Then I tried the same link with Safari, which at least gives the error message mentioned in this post, and that's how I get here.
I am using a very poor wireless connection, so I would not be surprised if the download would take forever, but I don't understand how both AppFresh and Firefox believed having got the whole file. And what does the Safari error mean?