Microsoft's track record of delayed software releases is causing enterprises reconsider the vendor's Software Assurance programme. 

Software Assurance provides a subscription service for Microsoft applications entitling customers to upgrade to new product releases at a discounted fee of 29 per cent per year for desktop software and 25 per cent for server software.

The plan provides Microsoft with regular software revenues during years in which it does not issue any major Windows of Office releases.

A Forrester survey of enterprises whose subscriptions are about to expire found that 26 per cent intend to cancel their plans. 

Only 11 per cent said that they will 'definitely renew' their contracts, and 13 per cent indicated that they will 'probably renew'. The remainder was 'still deciding' (31 per cent) or planning to renew 'only for some products' (18 per cent).

Delays in Microsoft products have undermined the economic benefits of the programme, according to the survey respondents.

The five years that it took Microsoft to develop and release Windows Vista ended up costing Software Assurance subscribers 145 per cent of the retail price.

The firm's server operating system is scheduled for release four and a half years after the launch of Windows Server 2003, meaning that subscribers will pay 12.5 per cent over the retail cost.

The value is even further eroded if the time that it takes to test new products and interdependencies is factored in.

"Many are questioning the future value of Software Assurance," said Julie Giera, a vice president with Forrester, in the report.

"The economics of buying Software Assurance (at 29 per cent of the licensing fee for desktops) for the next three years without any guarantee that they will recoup their investment, make holding off on buying new licences until actually needed an attractive option."

The analyst recommended that customers hold out for a better deal. Microsoft is facing a large number of Software Assurance renewal negotiations and might be prepared to offer discounts or add free goods.