Image quality will vary depending on what option you decide to use when backing up the DVD. When you strip out the extras, and stick with just one language and no subtitles, the quality is pretty much an exact replica of the original (there will still be some compression if the movie takes a lot of storage space). When you copy the entire disc, including the extras, the image quality can take quite a nosedive, especially if it's a DVD9 disc. The quality drop is not that apparent on a low resolution TV, but pipe it out to a HDTV or computer screen and the pixelation can be very obvious.
On the otherhand, some movies don't use more than 4GB of data. Star Trek: Nemesis for example was nearly flawless.
I'll have to admit that I was quite impressed with the quality, and it is more than suitable for backup purposes.
Final Words
Backing up DVDs is a touchy subject. The obvious reason for Hollywood's outrage is piracy. A lot of money is lost for every pirate copy of a movie when it is exchanged, and naturally, this is bad for actors, directors, producers and even consumers in the long run.
However, there are legitimate reasons why one would want backups. In a household of children (or negligent family members), the last thing you want is for anyone to scratch your Director's Edition of Nitro Commandos of Mars. You can make a backup of it, and let that one get abused, while your original stays safe.
DVD X Copy Express does its part of respecting Copyright laws, and DVDs created by the software still maintains some form of Content Scrambling System. The warning before each backed up DVD is as clear as day, making the viewer well aware that the copy is a backup, and not the original. The backed up content is still encrypted as well, and although experienced DVD backup users can circumvent it, a backed up DVD still has the same copy protection as the original.
As for the application itself, it is extremely easy to use, churning out DVD backups in under 20 minutes (speed will vary according to hardware and media used). The interface is easy to understand, and depending on how you make a backup, image quality can be a very close (if not perfect) match to the original.
For those of you who are familiar with DVD backups, and use the many freeware tools, as well as not really being concerned with the legal issues, then this program is not for you. DVD X Copy Express doesn't make backup copies "right" if you intend on distributing movies, or simply padding your movie collection, so if you fall into the latter categories, freeware is the way to go.
Those of you who are genuinely interested in making backups of what you own, and want the easiest method of doing so, this program is worth a look. The average price seems to be between so the monetary investment is not huge. Is it worth it in the savings of your time? I think so.

Pros: Works as advertised, easy to use, and a real time saver.
Cons: Same things can be done with freeware tools.
Bottom Line: For those of you with little to no experience backing up DVD movies, DVD X Copy Express is the easiest tool that I've used for this purpose. Everything is wizard based, and there aren't too many adjustments to make by the user to begin DVD backups.