VS SP1 - More than a Service Pack
I'm not sure how I would define a Service Pack these days but I'm glad to see that the VS team also uses this to add functionality. In Soma's words:
Not only were we able to fix the customer impacting bugs in this Service Pack, but we continued to add value to these products by putting in new features that they were asking for. A few examples of this are the .NET Client Profile which drastically reduced the size of the .NET Framework (by over 86%!) to allow for ease of deployment for .NET applications, support for SQL Server 2008 both in Visual Studio and through features such as the ADO.NET Data Services and ADO.NET Entity Framework, as well as multiple enhancements to ASP.NET and TFS. The performance and reliability issues we fixed in Visual Studio gives increased productivity to all developers.