I agree with the other reviews that this product has a minimalist interface but a robust OCR engine. The issue I had with it is, using the demo, the accuracy was very impressive. Okay, trial period over, time to buy; I paid online, downloaded the paid version (Aug. 28), and upon installing it, got a warning "the disk you chose contains a newer version of the software you are installing. Installing this software will replace a newer version with an older version." Since the trial version would no longer work, I went ahead with the installation (I should have hesitated as in the Installer, a page entitled Important Information only listed up to OS X 10.5, no mention of 10.6). I then launched the application, and proceeded to do a test scan on a book that had worked fine on the trial version. As with the trial, the scan proceeded and put up a window "Document Conversion" showing a progress bar that ended with the notation "Finished. 1 of 1 pages processed" But, the button "Finished" was greyed out so the process essentially ended there; All other menus were greyed out, so I had to quit the program via the Mac utility Activity Monitor. I didn't think to make a note of the trial version, but the (broken) paid version was 188.8.131.5278 Part: 718/4 (from the app's About menu, as a Finder Get Info does not include version information).
On the next launch I thought to see if there was an entry for checking for updates, and there was. I downloaded the update, it indicated it was compatible with OS X 10.6 and indeed it did not hang at the "Document Conversion" window; it was now version 184.108.40.20691 Part 718/5. I was then able to compare scanning/ocr'ing the same page, same book as I had done with the trial version, and noted that there were a few more errors with the full version. It seems that the trial version was better at automatically de-skewing the page. The full version also felt slower than the trial one.
I wrote ABBYY about this, they did respond and admit the following "FineReader Express for Mac trial was created after the full version of the software was, because there was a high demand from users requesting a trial version, therefore, when you install the full version it shows that is a [sic] older version of the software, but you are running the latest full version of the software." Conclusion: the full version that one pays for, even after using the Update feature, is older and slightly less accurate than the more impressive trial version. I'll continue to check the Update feature (can't set it to auto check, and the Preferences menu entry for all versions [trial, old full and updated full] were greyed out and in fact when reading the manual no mention of Preferences at all. Today, Sept. 6th, I did the manual update check and was advised that "There are no updates currently available for ABBYY FineReader Express Edition for Mac Build 3891." In sum, if you're impressed by the trial version, you may run into some install/use problems with the initial paid download and even a working update is less robust than the trial. Still, after trying 3 other OCR packages, ABBYY FineReader Express for Mac still has a strong edge for accuracy.