Many people know about the support lifecycle site at Microsoft. It contains information about the support policy for Microsoft products. It allows you to look up a specific version of a Microsoft product and to see when support for that product ends. It also explains the support phases that a product can travel through, and how these phases affect support for different customers. (You can read about the support phases here.)
Now that I work for Microsoft Services, this support page has become very important to me. I've discovered that many people DO NOT know that Service Packs also have a support lifecycle. Even though a product has support, a particular Service Pack may not. Let's look at an example.
Supposed that I am using SQL Server 2005. If we look this up on the lifecycle site, we'll see that SQL Server 2005 will be Mainstream support until 4/12/2011. We'll also see that it will be in Extended support until 4/12/2016. Looks like I'm covered, right?
What if I haven't installed any Service Pack? This is known as the RTM or SP0 release. Support for this release expired on 7/10/2007. Oops! No support! I could be in trouble. If I install Service Pack 1, then I'm a bit better off. I will have support until 4/8/2008. Service Pack 2 woud be even better. Since it is the most current release, it doesn't yet have an expiration date. (Other than the expiration date of the product itself, of course.) You can read about Service Pack support here.
So, as you can see, product support is determined not only by the product itself, but also by the installed Service Pack. Because no one should install a Service Pack without appropriate testing, it pays to use the lifecycle site and to plan your testing accordingly. Do let yourself get caught with an out-of-date Service Pack!