One of the things that makes word-of-mouth effective is that it's perceived to be based on authentic and commercially disinterested opinion. So, as soon as you sense that I stand to profit from you acting on my recommendation, you become more wary of my recommendation and less likely to act on it. (I've written about this in the context of blog marketing on my DJ Alchemi blog.)
In the music area, a couple of initiatives have started, with mixed receptions. Weedshare has been running a scheme for several years now, which encourages you to share digital music files with your friends by email, instant messenger or your website. They can listen to each file three times for free, but then have to pay to enable unlimited plays. If they do pay, you get a commission. It seems like a transparent model, and fairly simple in broad outline (though I think it gets complex in the details). The Digital Music News blog and associated comments give a mixture of opinions. It's fair to say that Weedshare hasn't exactly taken off and hit the mainstream, but that's possibly because (a) it has no major label music, (b) it uses Windows Media files (incompatible with iPods) with DRM, and (c) on the receiving end, illegal peer-to-peer sharing is more attractive, because there's no payment.
With BurnLounge, launched earlier this year, "music fans can use simple point-and-click technology to build their own fully functioning digital download store" (source). I think it's fair to say that the BurnLounge model has raised more controversy. Sceptical and suspicious blog posts on Digital Music News and the Digital Music Weblog have attracted an avalanche of defenders of the model, most of whom appear to have bought into it in a big way. I don't particularly want to get drawn into the controversy, but, as a bystander, methinks they do protest too much.
Amazon have been around long enough that they don't attract the same degree of suspicion as a new entrant. Also their affiliate programme is fairly well established and understood. They've now extended this with their aStore initiative (which is in beta, just to show how Web 2.0 it is). With aStores, any of us can set up our own store, branded with our colours and logos, promoting Amazon products and earning a commission on sales.
My hunch is that the transparency and relative simplicity of creating an aStore will make them quite popular. Just looking at Amazon.co.uk usage, there seem already to be hundreds of stores just a week after launch. Simple music stores include the Bad Robot's and Cyberextazy's. Deeper and more interesting are The Scottish Store, This French Life Shop and Egyptian Books & Music from Egypt (can someone just explain why Men Are from Mars, Women Are from Venus is a 'top Egyptian bestseller'?). These are niche aggregates of Amazon's offerings that Amazon itself would never have the in-house expertise to develop.
[Update, 4 September 2006: I'm not clear whether the recently announced MySpace download service will allow MySpace to sell other people's music, possibly in return for some commission. The Terry McBride quote at the end of this Wired News story — "We have a strong belief the next major retailer in music is the consumer themselves" — implies that it will. However, earlier in the same article, it says, "To get their music ready for sale, bands will have to upload their songs to Snocap's online music database. Once cleared by the company — a process to ensure someone isn't trying to sell music to which they don't own the copyrights — the tracks are available for purchase, Snocap said." (my emphasis) Anyone know for sure?]