This is Vista Home Premium 32bit; it came with Adobe Reader 8.1.2, which I fully updated, then replaced with Adobe Reader 9.0.0. Same problems either way. More info: Toshiba Satellite notebook, 3 GB RAM, 200 GB hard drive, AMD Turion X2 dual processor.
In about half the instances, a .pdf file that Reader has opened never shows up among files in the computer's Recent Items list (in the Start button). No idea why some do/some don't appear.
Also, both Reader versions freeze when one accesses the About option in the Help menu. Ctrl+Alt+Del is the only way out from that, apparently - not great. Only Reader freezes and requires using "End Task." All else keeps operating.