'Unreadable Disc' Error fixed...
The 'Unreadable Disc' errors that some users were experiencing was due to 2 factors:
A) The Matshita DVD Drive that is used in most MacBooks, MacBook Pro's, and iMacs are not high quality drives.
B) If you don't use high quality DVDR+DL media in your Matshita DVD Drive, the problem is compounded

This leads to the 'Unreadable Disc' errors on the Xbox 360. The solution is quite simple:
A) Use high quality media (i.e. Verbatim)
B) Use a high quality DVD drive (i.e. LG, Pioneer)

I purchased a LG Slimline DVD Drive and it works great. It is also much more quiet than the Matshita, and is USB powered for your laptop. I also purchased Verbatim media and that works well with the Matshita drive. Other users reported Aone media works as well.