OK but don't forget about markers, they seem to be the only way of labelling a section of clip with something unique. For example I want to not down that a character is talking about his time in Sheffield, he may be the only time that anyone talks about this so creating a keyword specifically and adding the section of it to it is a lot more fiddly than Commant+M and typing 'talks about Sheffield'. I sometimes have 30+ comments on a interview, I don't want 100s of keywords all with one thing in them.
Are you teaching editing or how to use FCPx. I have vary rarely seen them taught together (I am talking long form procedures and processes, not the technical aspects of how to use the software)?. Thinks get a lot more involved whn you go from a 5 minute short to a long form feature.
On the Compound Clip side of things I don't think FCPx (unlike avid) allow you to colour code clips (i.e. using colour coding so you can see where scenes start etc).. Within a act you may sequences (not to be confused with the technical term used in editing, where are scenes that live together and generally are moved together). Marking and labelling them is very useful so you can easily see where things are on the timeline and how long they are. Its a great way of managing and moving things around a long time-line, the compound clips can always be expanded later for fine cutting.
Also if you have a number of clips from the same media file and you rename one it renames them all (in the library). Again it may be a unique name for the clip so keywords are not appropriate. Markers seem the only way of labelling them.
Ben