We have experienced a very similiar problem actually. It is important for us to reproduce drawings at their correct scale, yet when we select a printer to plot to and apply the No Scaling option the preview window doesn't take into consideration the setting I've just tried to apply and ignores the paper size setup for the plotter. The plot preview window just shows what appears to be an A4 window upon a larger format page size.
This is utterly disastrous for us working in an engineering and surveying company wher drawings must be reproduced to scale. As it is we have no confidence in Adobe Reader X right now and immediatly reverted back to 9.4 after a network wide deployment. This utterly sucks Adobe. You have many competing companies biting at your heels for share of the PDF editing and reading market yet you should be setting the gold standard for PDF applications having derived the standard in the first place. The fact you'd finally introduced sand-boxing I thought was going to be a god-send and we can go back to a single PDF application as your security flaws are a disaster waiting to happen - but this bug I'm afraid is just plain embarrasing!!
This is a major problem for us as well. Being an Engineering / Architectural company. I sure hope Adobe is fixing this.
I can't believe we're the only ones posting about this - shocking Adobe - SHOCKING!!!!
Has the latest patch 10.0.1 fixed this issue for you guys???
I've just tried it yet the bounding box does not appear to change how far it stretches across the PDF file when you change the printer's paper size when you want "no scaling" on!
Also i believe this a thread covering same issue here, which actually has Adobe's attenttion: http://forums.adobe.com/thread/764819?tstart=60#