I upgraded to Reader X from Reader 9.3.4 and I'm extremely disappointed with it. Basically it broke a lot of stuff and didn't add any new features that I can tell. Here's the things that are now broken:
Add to that the above that Reader X is extremely slow and I'm very close to going back to 9.3.4.
This version is unreliable indeed. Better not use it!
Today I downloaded Adobe Reader X 10.1.0 to view technical drawings in PDF made by AutoCAD 2013. Viewing is OK, but when it comes to printing, some lines are missing! This happens with printing both to paper as to PDF (using PrimoPDF). Use an old Adobe Reader or use another brand (I like Bluebeam Vu).