Alex Ross discusses on his blog a project by Eric Grunin to document changes in the performance of Beethoven's Eroica Symphony over the years. His visualization of changes in tempo in the first movement over time are particularly interesting:
(Red dots represent performances that take the repeat at the end of the exposition; blue dots do not).
Grunin finds all sorts of new and interesting data to analyze. I especially wanted to link to it to show that there is a lot of amazing projects in computer-aided musicology still to be done that do not require the use of analysis of music as symbolic data (as music21 does)