UPDATE 2nd February 2016. Ancestry has reconsidered its decision and has provided two options for users who wish to retain an offline copy of their family history research -
The full details of the orginal announcement can be read on the Ancestry Blog but the key paragraph is quoted below -
True to this focus, we've taken a hard look at the declining desktop software market and the impact this has on being able to continue to provide product enhancements and support that our users need. With that, we've made the decision to stop selling Family Tree Maker as of December 31, 2015. Our subscription business and website, on the other hand, continue to grow and we are doubling down our efforts to make that experience even better for our Ancestry community. Ancestry will continue to support current owners of Family Tree Maker at least through January 1, 2017. During this time, all features of the software, including TreeSync, will continue to work, and Member Services will be available to assist with user questions. We will also address major software bugs that may occur, as well as compatibility updates.
Why have Ancestry done this?
Note - This is pure conjecture as I don't have a seat on the board at Ancestry.com!
Cost. It costs money to staff a helpdesk. It costs money to pay developers to add features, fix bugs and keep up with new versions of Microsoft Windows. Ancestry have made a judgement that this cost is not worth paying in order to keep its FTM users happy.
The Cloud - it's the future. Having all your services up "in the cloud" is the trendy thing to do these days. For consumers this works well when your services are being provided by a company you can depend on maintaining those services indefinitely or where those services are easily transferred to another provider. The only problem is that a) Ancestry have a track record of getting people to sign up to stuff and then withdrawing it a few years later (remember the first DNA service they offered and then dumped?) and b) it isn't straight forward to move data to another provider as users have been persuaded into using proprietary features that aren't covered by the GEDCOM file transfer format.
The Implications for You
OK, so Family Tree Maker won't stop working overnight so FTM users have some time to plan what to do next.
Make sure you have all your research data. Currently Ancestry provides the facility for you to export a GEDCOM file from the online pages but they do not provide a facility to download all the images associated with those records. However, if you ensure that FTM has successfully synchronised data in both directions before Ancestry turn off the tree sync facility then the images, even if they were uploaded to the web based application, should be stored in a sub-folder of your Family Tree Maker folder on your hard disk.
Back it up. You may be a little wary of cloud based services at this point but using an online storage facility such as Google Drive or Dropbox doesn't have the disadvantages of a proprietary application such as Ancestry offered as, if the service is discontinued or there is something you are not happy about, it is generally a simple matter just to move your data to another storage provider.
Get another Family Tree Application. There is no real rush to do this - but at some point, it is likely that a new version of Windows is going to break FTM. It is also probable that certain features of FTM will stop working over time - tree sync and the integrated Ancestry Search and Merge facilities will most likely be the first casualties. Maybe sometime soon there will be a standard way of exchanging family tree data together with the rich media associated with it. It looks like there is a work in progress with the GEDCOM X specification but it maybe some time before this is adopted by all the online and offline Family Tree software applications.
The Implications for Ancestry
Content. Much of the content on Ancestry is supplied by their subscribers. Given this decision by Ancestry, it is going to be a long time before users will trust them as the safe place to store all their data. Indeed, it is likely that users never did trust them as a safe place to store their data but because FTM just sync'd their tree without any effort on the user's part, they were just happy to let the software get on and do its thing. The net benefit was that Ancestry got a whole bunch of user supplied data that they could use to lure more customers in. So Ancestry will lose an important source of new data - but also, given the tone of the comments on the announcement page, they may lose a lot of existing data provided by their current customers as they leave Ancestry in their droves.
Trust. Let's face it; this move can only have a negative impact on the trust of Ancestry's subscribers.
Revenue. OK, they will save a few dollars on development and support costs - but they will lose subscribers over this (the comments on the announcement make this abundantly clear). They are also dropping a major feature that differentiated them from the competition - so subscribers will no longer have a reason to be loyal to Ancestry - they may as well go anywhere.