It might be interesting to see what value the taxman puts on my bedroom antics (I'd like to think my services appreciate rather than depreciate over time...)

However the taxman has a useful trick, in that she can tax based on the (monetary) market value of the thing being "bought". So if you have sex with me in return for me developing your (£xxxx worth) iOS app, and the taxman finds out (during audit : "who developed that app, and how much did you pay?") she'll WILL come knocking on my door for payment (in cash, unfortunately, the Queen doesn't accept nookie). In the UK the taxman has a long history of investigating and taxing non-monetary transactions.

Casual transactions between the public will probably slip under the radar, but try earning any significant "sex and music" as a business or self employed, and you run a reasonable risk of getting caught out.

A sex and music based economy sounds great.

Though thinking about it, as a non-musical nerd I'd probably starve pretty quickly.

It is also worth noting that if said music-based economy was a one in which the music was digital, most likely there would be rampant inflation due to counterfeiting.