The Nexus unified the filesystem, and therefore cant give USB block-level access. MTP was the only way to go unless you want to have a separate partition, which leads to the terrible 'is the app on local or on sd?' situation.
Here is the situation described: http://www.electronista.com/articles/11/11/19/galaxy.nexus.f...
For mac users, you want this tool: http://www.android.com/filetransfer/
After having the Galaxy Nexus for 2 weeks, the phone no longer feels large in my hands, but the Nexus S it replaced looks ancient and pathetically tiny/low-resolution.