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Last week the music streaming service Spotify got the kind of endorsement money can't buy. At Facebook's F8 event, Spotify's founder Daniel Ek was invited to share the stage with Mark Zuckerberg, and explain just how "awesome" it was going to be to share your music tastes with your friends.

That privilege was not extended to Facebook's other music partners, and it looked at first as though this was a deal which offered a lot more to the European start-up than to the social network.

Now though it is becoming clear that there may have been a price to pay, with Spotify apparently tying its whole future to Facebook. The risk is that this will alienate its existing customers who are already up in arms about one aspect of the deal.

If you go and try to sign up now you will find that a condition of joining Spotify is that you are also a member of Facebook. The argument is that it's all part of the "deep integration" between the two services and users will become addicted to sharing in a seamless way their music listening habits.

Now you would imagine that there would be an almost perfect overlap between the 800 million strong Facebook crowd and the kind of people who might be interested in a streaming service. Nevertheless the reaction from many fans of the music firm has been a mixture of shock, surprise and an almost tearful rage.

Here's a selection of messages I received when I asked my Twitter followers about the new policy:

"I think I'll probably close my account."

"It's ridiculous - why would a social site insist you have another social account to use it?"

"Spotify were like the innocent of the internet, then in a parallel move they sold out to Coca Cola."

"It is utter madness."

A lot of this appears emotional rather than strictly logical. After all, if you're already on Spotify you won't need to sign up to Facebook - or link your account to it. I put that to one user, who said it was a matter of principle - nobody should be forced to use Facebook to get access to Spotify.

And, just like the Facebook users who accuse the network of selling out to big business, a lot of the anger seems to come from those who appear bemused by the idea that an internet firm would actually need to make money.

Spotify has tried to explain the move by asking users to "think of it as like a virtual 'passport', designed to make the experience smoother and easier, with one less username and password to remember."

But what is clear is that the whole idea of sharing your music tastes with the world - or "creating an amazing new world of music discovery" as the firm puts it - does not appeal to everyone. That I can understand - if you're relaxing with some cheesy 70s pop, do you really want your much cooler mates to know that?

Spotify's founder seems to realise he has a big PR problem on his hands. Daniel Ek has been busy on Twitter over the last 24 hours responding to complaints about the Facebook issue. Here he explains the strategy:

"We want to remove barrier to sign-up and create a more seamless experience. As we think our users are social."

But there is also a hint that the policy could be changed:

"We'll try lots of things, and probably screw up from time to time, but we value feedback and will make changes based on it."

My suspicion, however, is that Mr Ek is none too worried about the threat of desertion by those horrified at the Facebook integration.

A much bigger concern will be that too many people join his free service - now open to all those American Facebookers - get used to the idea of sharing friends' music on the social network and never get persuaded to upgrade to the paid offering.

Even given the minuscule licensing fees paid to artists each time a track is streamed, that could prove very expensive.

But Daniel Ek and his team should be satisfied with their work over the last few months. After all, Spotify's recent history, with new markets entered and fans rushing to condemn changes in the service, looks like a miniature version of what Facebook has gone through over the last few years.

Now, like a pilot fish attached to a great white shark, the smaller firm has entrusted its destiny to the social networking giant. It just has to hope that it can feed itself for a while - before it gets eaten.