Every Microsoft product has a lifecycle. The lifecycle begins when a product is released and ends when it's no longer supported or sold. Knowing key dates in this lifecycle helps you make informed decisions about when to upgrade or make other changes to your software
Most service updates to Microsoft Dynamics CRM are done via Update Rollups. An Update Rollup is a tested, cumulative set of hotfixes, security updates, critical updates, and general updates that are packaged together for easy deployment. Update Rollups are normally broken up and applied for each individual component of your CRM system, such as Client (Outlook), Server, Email Router etc.
As at 26th November 2012, these are the support timeframes for Microsoft Dynamics CRM.

So from that table you are now probably asking “What is the difference between Mainstream and Extended Support?”. Well below I have the answer for you.
From the list you can see that next up is Microsoft Dynamics CRM 4.0, which has a mainstream support end date of 9th April 2013.• Mainstream support - Microsoft will offer mainstream support for a minimum of 5 years from the date of a product's general availability, or for 2 years after the successor product is released, whichever is longer. For example, if you buy the new version of Microsoft Dynamics CRM and five years later another version is released, you will still have two years of support left for the previous version.
• Extended support - Microsoft will offer extended support for either a minimum of 5 years from the date of a product's general availability, or for 2 years after the second successor product (two versions later) is released, whichever is longer. Microsoft does offer a note here though: Extended support is only available for commercial customers.
I have made an assumption here that if you are reading this article, then you are not still running v1.0 or v1.2 in your production environment. Comment on this blog if you are.