I just upgraded to 12.10 and noticed that my media hard drives are mounting automatically. In the past I would have to mount them manually. Is this an upgrade feature?
That depends, it does so for drives that are plugged after booting up but not for the ones that were plugged in before I booted ubuntu. So I would say it is a feature not a bug.
Similar behaviour was available in Ubuntu 12.04 “Precise Pangolin”: a filesystem on an external USB hard disc would mount inside /media
On that basis, I couldn't call this a new feature in 12.10
The feature has been there for a long time, if I didn't remember wrong, it was there in 8.04. However, in early releases it was partially working. Sometimes you'll have to manually mount the USB drive.
Normally if you plugin external USB storage, it will be automatically mounted under /media.