Mythtv:Skipping Commercials
LinuxMCE's default MythTV integration does not automatically edit out commercials after recording, though MythTV does have this ability. In its default state, MythTV will record a show, and then after it is recorded run it though a process which attempts to Identify commercials. It saves this information, but nothing is done with it. After this step is complete, a job runs which adds the new recoding to LinuxMCE's media database so it will show up in the datagrid on the orbiters.
There are, however, ways to Automate commercial removal, as well as manually remove them from old recording that you didn't have it set to do automatically for. I recommend learning both, as there is no replacement for Human Intelligence when it comes to marking commercials, though in my experience MythTV does a pretty good job of it.
Automatic Commercial Removal(AKA Automatic Transcoding)
Manual Commercial Removal and Transcoding