Well the 2006 DVD release has been out over a month now. As is the custom whenever Star Wars gets a release, someone has to make a list of what's wrong with it!
(List collected from various posts on the forum. Please correct any errors I've made. I'm planning on adding screenshots of the flaws at a later stage).

Since this DVD comes from the old definitive collection laserdisc master, many of the flaws mentioned here are equally as relevant.

The DVNR or dirt concealment process that was used in mastering the THX laserdiscs caused a plethora of motion artefacts - trails, detail smearing and ghosting of bright images onto succeeding shots. Since the same master was used for these DVDs, the same effects are visible.
Since the transfer is non-anamorphic, widescreen TV owners will need to select the "zoom" display mode to view in the correct aspect ratio (sometimes also called "cinema" mode). This results in Greedo's subtitles being lost off the bottom of the screen. Although some TVs have a "subtitle zoom" display mode that will fix this, this causes the "letterboxed" portion of the screen to be postioned higher up. Having unsymettrical black bars is aesthetically displeasing.
Greedo's subtitle for the line "it's too late" is missing from the PAL region 2/4 discs.
A distracting left/right wobble - known as "gate weave" - is present on this transfer. This is caused by enlargement of the film sprocket holes over time. For Star Wars, the shot of the original theatrical opening crawl and Star Destroyer flyby is a new transfer (the laserdisc featured the "Episode IV: A New Hope" crawl). It has been reported, by someone who is an authority on visual effects, that a "fake" gate weave has been added to this first element. Perhaps this was in order to match the look of the new element to the natural weave present in the rest of the transfer.
A problem with horizontal field movement during the telecine process caused 'jaggies' in the Definitive Collection transfer. Instead of fixing this properly, i.e. making a sub-pixel horizontal adjustment between the fields, the DVD has been mastered with a vertical blur to mask the jaggie effect.
IVTC errors - the master video will have had 3:2 pulldown applied to produce the NTSC framerate of 29.97fps. For the DVD, the video was inverse telecined (IVTCed) to convert to 23.976fps. Unfortunately there were some cadence errors in the master, resulting in some flickering artefacts on R2D2 in the scene with Ben and Luke after the Sandpeople attack. These artefacts are visible when viewing on a computer or a progressive display.
The image on the DVD is extremely grainy. Opinions vary on this - take your pick:
- artificial "grain" has been deliberately added to the image
- it's a by-product of sharpening applied to the laserdisc masters
- the films have always been grainy, it just looks worse on DVD because this format reproduces more detail
The PAL (region 2/4) DVDs are upscaled from the NTSC masters. Not necessarily a flaw, however this is a very lazy practice in DVD mastering. An equivalent PAL master was used for the 1995 laserdisc releases in France and Germany; this master could have been used for the PAL DVDs.
The German audio track was faulty on some discs. In chapter 13 of ANH when Luke, Han & Chewie wait for the elevator to the detention area, the announcements in the background are missing - as well as the lines "Ich kann in diesem Helm überhaupt nichts sehen (I can't see a thing in this helmet)", "Das wird nicht funktionieren (This is not gonna work)", "Warum hast du das nicht gleich gesagt? (Why didn't you say so before?)" and "Ich habe es gesagt (I did say so before)". A replacement disc with fixed German audio is available from 20th Century Fox Home Entertainmemt by emailing info@tcfhe.de.