Here's my approach to labeling song sections, by repurposing a MIDI track and using its clips to indicate those songs sections (see image below).
Basically I create some dummy information on a new MIDI track, and then I extend out the MIDI Clip to represent a section of a song. I can then use that clip to help select a section of the song for rearrangement purposes or just simply to identify the section more clearly.
True, I could use markers for this purpose, but I find they get very cluttered with all the notes I want to make. However, by using a MIDI track for this information I can create as many tracks and spread out the marker type information (e.g. song sections, to do reminders, etc.)
I'd love to see Sonar incorporate non-audio/midi tracks that can hold this type of information. What do you think?
http://variousartist.com/sonar/PeterMatuchniak_Sonar_InformationTracks.jpg 
It would be cool if we could have new types of tracks for these purposes:
Existing track types:- audio
- MIDI
Suggested new track types:- marker/arranger (song sections)**
- To Do list
- lyrics
- chords
- BPM ruler
- SMPTE ruler
- blank (for spacing large projects)
Etc
**Selecting an arrangement section would automatically select the entire set of tracks within that time-selection. And moving that arrangement/marker clip would automatically move everything else too. Simples!
Regardless, you would be able to add in multiple track types of the new kind. So I could have multiple marker/arranger tracks (one could be used to describe low level song sections, such as verse, chorus, etc., and another could be high-level sections, such as part 1, part 2, etc.). I could also add in multiple BPM/SMPTE ruler tracks so that these line up against any audio/midi track for ease of reading etc. (this would be especially useful if a I had a movie sound track that required noises at a particular time, whereas another audio track was lined up against an BPM ruler for musical purposes). Etc