Sitecore 6 has retired the masters term – a fine decision which hopefully will remove a lot of the obvious mistakes made when designing Sitecore 4 and 5 solutions, e.g. like assigning masters and layout directly to a content item.
The concept has been substituted by the possibility to assign templates directly templates (i.e. “Which templates can be created under this page type” instead of “Which prefilled items can be created under this page type”). The prefilled data on the master (which was copied to the items) can still be applied using Standard Values (which was there in Sitecore 5 as well). Standard Values are made even more powerful than in Sitecore 5 since it now derived through all inheritance levels, i.e. if DerivedItem is created from DerivedTemplate which derives from BaseTemplate, standard values set on BaseTemplate also applies to DerivedItem. This means that you can e.g. set a layout on BaseTemplate and thus all the derived templates will now have a standard layout which you apply changes to.
With this and other features, Sitecore 6 has made some nice changes to force developers to design better Sitecore solutions by applying content reuse and thus makes the solution easier maintainability. But there are some issues: Sitecore 6 no longer indicates whether a value is a standard value or actually applied to the item (see below). In my opinion this is a major flaw. It is vital for developers and administrators to be able to instantly determine whether a value should be changed directly on the item or on the template, thereby allowing them to think about whether the change should be universal or local change. An ugly dent in the before mentioned “changes to force developers to design better Sitecore solutions”. Thankfully the designer of the DBBrowser (hail!) has not been so rash – but this is still not a tool I would like my users (even the super-ones) to see. Hopefully this will return in an upcoming hotfix.