It should have been the biggest launch of 2007.

Abseiling acrobats formed a 'human billboard' high above Manhattan, fireworks illuminated the Grande Arche at La Defense in Paris, dancers performed all around the Taj Mahal and Bill Gates was on hand at the British Library for the UK launch - Microsoft Vista was upon us.

Everything associated with it was big. It was a 36-hour event that marked the start of a $500m (£257m) marketing investment, designed to generate more than 6bn global impressions and sales that will eventually exceed $70bn (£36bn). Yet for all the scale and budget of its launch, the impact of Microsoft Vista has been, well, small.

Those with good memories will remember the big headlines and long queues that greeted the introduction of Windows 95 some 12 years ago. Vista was a very different story; there was distinct indifference from the world's media.

According to John Bentz, senior vice-president at Waggener Edstrom, one of Microsoft's key PR agencies, the goal of the campaign was to create a 'visceral experience'. He said: 'We wanted it to drive broadcast attention, and to do that we had to do something significantly bold and daring.'

Despite this big-launch talk, two weeks later, Vista seems to have all but disappeared. Most of the trade press has remained singularly unimpressed, while the popular press seemed only mildly interested in Microsoft's attempts to generate buzz on launch day.

Then there was the crap slogan. 'The wow starts now'. We all know that marketing is more than a snappy strapline, but rarely in the brave field of marketing has so much been invested in so little. If you believe all the guff from Microsoft, the Vista launch has been years in the planning. If this is what years of planning generates, God help Microsoft if it ever has to go to market within months.

The big question is not whether the Vista launch was a major disappointment, but why it had such a small impact, given the funds, scale and time ploughed into it.

One possible explanation is that Vista is not as important to Microsoft as we might be led to believe. Despite the claims of chief executive Steve Ballmer that this was the biggest and most important launch in the company's history, the reality may be that a bigger launch is on the horizon. Vista is arriving two years late, which could mean it will soon be eclipsed by a more advanced Microsoft operating system. Rumours are already circulating about a new offering, codenamed 'Vienna', which, according to several Microsoft contacts, could launch as soon as 2009.

Another possible reason for the poor performance of the Vista launch might be the size of the budget - it may have been too big.

When marketers get too much to spend, they get lazy, big and ineffective. They start laying out for hugely expensive and ineffective executions and pay little or no attention to positioning or marketing return on investment. Over-investment in marketing is a relatively rare occurrence, but when it happens, the end result is the same as the much more commonly occurring scenario of under-investment.

Perhaps the most intriguing explanation for Vista's launch failure is a much broader one. In contrast with 1995, we are living in an inherently interactive, multi-vocal and polysemous world. The days of the big global launch may be over. This is the era of YouTube, blogging and co-creativity. The great irony of Vista is that the interactivity and connectivity it was designed to offer its users might also explain its apparently very big, but actually very small, launch.