Hi everyone!
I also have a Nikon D3000 and a macbook,
For me the solution is to use aperture (or iphoto)
And going to:
Preferences> Import> 'when a camera is connected, Open:'
Then choosing iphoto, aperture etc.
If it does not work strait away I leave my 3000 connected by usb + on, then restart and open aperture and the photos are there!
Hopefully this works for you!
(it's basically trial and error or a restart solution, it never seems to be too long before the two talk to each other 😛)