DVD Playback is extremely pixelated an unwatchable for certain DVDs, e.g. Star Wars Episode II: Attack of the Clones.
PowerDVD is installed on the system and it plays all DVDs just fine. Media Center indicates in DVD Playback Options that it is set to use the Power DVD filters. Between 20-30% of CPU is being used during playback, so that doesn't seem to be the problem.
I did some more testing and discovered the following: This also occurs on PCs that have other DVD filters installed (e.g. WinDVD). In each case the DVD app plays teh DVD fine, but MC has the problem even though it is using filters from the DVD app. This problem occurs not just with the most recent builds of MC11, but also with builds going back at least to 11.168. It doesn't occur with all DVDs, but for those it does occur with, it happens all the time (i.e. reproduceable with every play). As mentioned above, one common DVD that this behavior occurs all the time with is Star Wars Episode II: Attack of the Clones. Hopefully this DVD is commonly enough owned that someone else will be able to reproduce the error or determine that they aren't experiencing it.