The beta I got on the trail was that from Vienna to Budhapest (i'm pretty sure that isn't spelled correctly), isn't nearly as well marked as the part I rode. I met some Italian guys who were doing the whole thing, and they were a bit concerned about the last leg to Hungary. As it was, the signs weren't as closely spaced as I would have liked. Routinely, I would be absolutely sure I was lost ... about ready to turn around ... decided to keep going just a little further... then there would be a sign... tee hee.
I think the last leg Vienna to Budhapest would be awesome though. Travelling through such a historic part of Europe would be phenomenal.