For the longest time, Microsoft had something of a poor reputation as a software developer. The issue wasn't so much the quality of the company's software but the way it was developed and delivered. The company's traditional model involved cranking out a new major version of Office, Windows, SQL Server, Exchange, and so on every three or so years.
The releases may have been infrequent, but delays, or at least perceived delays, were not. Microsoft's reputation in this regard never quite matched the reality—the company tended to shy away from making any official announcements of when something would ship until such a point as the company knew it would hit the date—but leaks, assumptions, and speculation were routine. Windows 95 was late. Windows 2000 was late. Windows Vista was very late and only came out after the original software was scrapped.
Read more at ArsTechnica.