New in 10.1!
Tired of scrolling through all the possible projections when you only use about 3 or 4 of them? In ArcGIS 10.1 you can now save commonly used projections as a ‘favorite’.
Next time you are specifing a projection for a dataset you can mark the projection as a 'favorite' by simply clicking the 'star icon' in the top right corner of the dialog box.
Next time you need to specify that projection, simply look for it within the 'favorites' section.