Here are some of my favourite new tools and improvements that have come with the 10.1 release. These should make your mapping and workflows just that much more enjoyable.
With ArcMap shipping with over 4000 projections, it is easy to feel a bit overwhelmed, especially if you are a new user. Although you have always been able to save the frequently used projections to your favourites, you can now input keywords and find exactly what you are looking for. If you have no idea what you are looking for, you can even let ArcGIS use your current extent to suggest the best projection.
2.Enable Editor Tracking
Trying to figure out who moved that feature without telling you? Now with Editor Tracking enabled on your feature class, any new features or modifications will be logged with the username and time/date of creation or modification. This works with SDE databases as well. This is going to make your metadata housekeeping a lot easier. Note: This will not tell you if a feature has been deleted – best to use versioned geodatabases for that.