I came across a thread in another forum that I use which came up with some interesting information on selling music online (and other related matters such as illegal copying etc etc) which you may find interesting if you didn't come across it. Interview with Will Page has links to some background on it but here is a summary which was posted by Colin Lazzerini which I can't improve on so quote -

"In a famous 2004 Wired magazine article, Chris Anderson borrowed the old post-war statistical concept of a frequency distribution with a long tail and re-made it in the form of a notion to illuminate internet media business successes. Low operation and inventory costs, according to Anderson, allow significant profit to be realized from the sale of small volumes of hard-to-find items to many customers, rather than large volumes of a narrow range of popular 'hit' items.

And the existence of the Long Tail, as a sustaining demographic purchasing a large number of "non-hit" items, thus became an article of faith in the new 'indie' ideology

This received wisdom, however, that diverse specialised items – though individually less popular - will together outsell mainstream 'hits', has now been profoundly compromised by actual analysis of one year's music revenue in a study led by Will Page, Chief Economist for the UK's royalty collections agency the MCPS-PRS Alliance.

Here is the sad grounded truth about the digital universe:

* Of the 1.23 million albums available on-line, only 173,000 were ever bought and paid for – the remaining 85% failed to sell one single copy.

* Of the 13 million individual tracks available by internet sale, only 20% were 'active', in that they managed to sell at least one copy.

* More than 10 million tracks failed to find one single buyer.

* Approximately 80% of sales revenue came from around 3% of these active tracks – numbering about 52,000 – the 'hits' which powered the industry.

* Only 40 tracks sold more than 100,000 copies, and accounted for 8% of the business.
(In the physical world, 40 tracks could make up just 4 albums).

The Two Main Lessons:

* The general rule for all inventory on the digital shelf is 80/0.38 – that is, 80% of revenue is generated by sales on only 0.38% of all available tracks.

* 80% of individual tracks sell nothing at all.

In their brief report on this research, The Guardian cheekily quoted Sturgeon's Revelation (they called it 'Sturgeon's Law') that "90% of everything is crap" – which I found pithy, appealing, and potentially perfectly apposite."