I get this question all the time because, let’s face it, it’s a significant decision. For example, an Enterprise Agreement (EA) renewal for an enterprise with the main desktop suite on, say, 10,000 PCs could cost around $1,500,000 per year. So what do you get for this outlay? You’ve already purchased a perpetual license for the relevant Microsoft products via your original EA, so the renewal is merely an extension of the maintenance element, which Microsoft calls Software Assurance (SA). Like most terms in Microsoft licensing, SA looks like an industry standard concept, but has sufficient Microsoft-specific nuances that confuses customers. The key differences from most vendors’ software maintenance offerings are that SA:
Is not tied to product support. Customers that aren’t paying SA still get access to patches, and can purchase additional support services from Microsoft or its partners on a time & materials basis.
Delivers upgrade rights that live on after the agreement expires. Customers earn rights to any version that Microsoft releases while they are on SA. So, for example, a customer paying SA on Microsoft Office for the next 12 months will earn the right to the next version, Office 14, due out at the end of 2009, even if it doesn’t intend to actually upgrade to that version for another 3 or 4 years
Includes many additional benefits that, though hard to value, are far from worthless. For example, the extra training, online e-learning and rights to use the same version on a home PC will certainly translate to more effective use of the software and enhanced user productivity, but it's very hard to give that a dollar value.