Developers have questioned the commitment to openness in Microsoft's Live Mesh service, which is designed to bridge the offline and online worlds.
The company's new service, that will synch all of a user's devices and applications to produce a seamless framework, was unveiled at Web 2.0.
Microsoft has said the service will use open standards and be rolled out to Windows machines, Macs and mobiles.
But developers at the conference said they needed more detail about openness.
Web 2.0 is one of the leading web development conferences
"As long as they innovate and it is an open platform that is compatible with other devices and other companies like Apple then I think it's great. I think they realise this and that they have to add value to people or they won't be able to keep up the strength of their brand."
Sam Pullara from Yahoo was not impressed by what he saw in the 15-minute demonstration, and he said that did not have anything to do with Microsoft's bid to buy the company he works for.
"I am a Mac man and frankly I have completely given up on Windows. To me it looks a lot like dotMac for the Apple and I think it will be a lot harder to execute well because Windows machines are just so different from one another."
Microsoft's Live Mesh general manager Amit Mital told BBC News that the firm was committed to openness and said there was a need for developers to get on board.
"We hope people will look at the platform and the capabilities and think about new imaginative ways of building applications that will benefit our customers."
At an earlier demonstration of the product to an audience of developers, he said: "Today we live in the world of the web and the web is at the centre of everything we do.
" It is how we connect with the people we care about, access the data that matters to us and also accesses many of the applications we use on a daily basis. And the way we connect with the web is via a number of devices."
Live Mesh is being privately tested by a core group of about several thousand with a public test expected later in the year. Over the next couple of days those attending Web 2.0 will be able to give Live Mesh a run for its money.