Interesting. As a player of piano, woodwinds, and others I've gotten used to different systems of scribbling over the staff to convey something that's not metadata but not primary info. Well-tempered Klavier is a good bad example, there's all kinds of scribblings about what Bach intended, including argumets about incidentals (is a note flatted or not?) (and what's the umbrella term for trills, grace notes, flourishes like that?). It's actually much harder for wind and strings, where infinite pitch/tonality /attack/decay combinations are possible, e.g. lipping up or down on a single reed, squeaking, honking, sibillant, and I'm pretty sure there's no way to write down the loops i get on fretless guitar, bass and cello.

Also I've been trying to get used to Don Ellis quarter tone system, and work thru haskell school of music (fantastic book, for anybody interested not just in notations, but production, composition and capture(A/D conversion/DSP etc. Also shoudl read books by Gould and Read someday:

http://www.amazon.com/Behind-Bars-Definitive-Guide-Notation/...

http://davidvaldez.blogspot.com/2012/09/quarter-tones-by-don...

http://haskell.cs.yale.edu/?post_type=publication&p=112