Currently Being ModeratedMar 8, 2013 4:42 AM (in response to Polecat48)
Yes, Aperture 3 can upgrade your Aperture 2 library.
But as a precaution it is strongly recommended, that you ensure that the Aperture library has no issues, before you migrate it to your iMac. Use the Aperture Library First Aid Tools to repair the permissions and to repair the database in Aperture 2, before you copy the library to your iMac.
To run the First Aid Tools hold down firmly the option and command keys (⌥⌘) while you double click the Aperture icon. Be sure to keep a working backup of the library, before you open it in Aperture 3.
Aperture 3 will upgrade the library to a new format. After that you will no longer be able to open it in Aperture. Also, some of your Aperture plug-ins may no longer be working on your iMac.