First of all, Rollup 12 and Polaris are not the same thing. Polaris is the codename for the December 2012 Q4 release of Dynamics CRM 2011 Online. Rollup 12 is available for On-Premise customers, which includes some but not all of the features included in Polaris. As with other Dynamics CRM rollups, rollup 12 contains various bug fixes, and has a corresponding Server update, Outlook Client update, Email Router update, and so on. On-Premise customers can Download and Install Rollup 12 now.

What are the benefits?
Polaris and rollup 12 include several new features that really make it worth upgrading. The most obvious new feature is the long awaited cross-browser support for web access. This means users and customisers can now access CRM using any of the major browsers (Google Chrome, Mozilla FireFox, and as always Internet Explorer). Polaris (online only) also introduces new process-forms for the Sales and Service entities, which provide a smoother, flat user interface designed to keep everything on one screen and eliminate pop-ups.

 What is Polaris and Rollup 12 in Dynamics CRM 2011

Is there going to be any impact on Users?
Certainly if you have existing users that are used to the 'classic' CRM forms, the new Polaris process-forms may be a little overwhelming at first. Fortunately, there is an option to switch back to classic forms which will be more familiar for them. Because rollup 12 and Polaris introduce cross-browser support, some of the 'unsupported' customisations that worked with previous rollups may not work anymore, so these should be reviewed and updated if necessary.

 What is Polaris and Rollup 12 in Dynamics CRM 2011

Is there any cost?
There is no associated cost to upgrade to Polaris or rollup 12; as with any other rollup it is simply just an update that needs to be applied to your server/outlook client/email router etc. If you are a CRM Online customer, your CRM server will have already been upgraded to Polaris, as Microsoft manages the server updates without you having to worry about this yourself.

If you have extensive customisations in your system, it may be well worth going through end-to-end to ensure everything is still working as expected. Also if you wish to use the new process forms in Polaris, you may need to re-customise these, as the process forms will not include your existing form customisations by default.