Does anybody know some interesting practical applications of PCA?
Not sure how "interesting" you'll find it, but PCA (and more generally, Factor analysis[0][1]) has been used for decades analyzing data from market research surveys.
Much of the process behind this analysis dates back to the late 1960/early 1970s at advertising agencies (notably Grey Advertising[2]) and market research suppliers like Grudin/Appel/Haley (all the name partners are long dead. but the firm continued as AHF Market Research. Not sure, but I don't think they exist any more).
These methods expanded within the industry and as computing resources became more generally available (back in the 60s/early 70s, it was all Fortran IV on punch cards, batch submitted to IBM/CDC mainframes), becoming pretty much de rigueur in the marketing/advertising industry by the mid 1980s.[3]
[0] https://en.wikipedia.org/wiki/Factor_analysis#In_marketing
[1] https://www.qualtrics.com/experience-management/research/fac...
[3] Source: Both my parents were involved in adapting such multivariate analyses for marketing purposes back then, and I worked in the industry for five years back in the late 1980s/early 1990s.
Edit: Fixed prose.