with regards to the removal of that feature apple care and customer support assures thats not the case as they have called me at least 5 times the last 3 days to "check on the situation"
unless they unknowingly got a bad batch of audio ports or just missinterpreted that it actually doesnt do what they say.
can anyone attest to the fact they have actually used to audio in feature and it worked properly through head phone jack?
Yes, I have used it -- the confusing part is that this is mainly an audio out port, but just like on many phones, it also has an input if the correct cable/connector is used, specifically a multi-axial in/out cable like the ones that come with the headphones for the iPhone. I believe these connectors have four conductors (wires/connections): 2 for left/right stereo audio output, 1 for mic input, and 1 ground wire (I think, well that's how I would have engineered it anyway). If you compare the connectors for these headset with mic connectors to those without a mic, you will notice fewer rings on the ones without the mic.
If you plug in a standard 2 channel stereo input cable to this port, the system will sense fewer conductors and think there is an audio output for a pair of headphones or speakers. If it detects the third signal channel it will assume there's a headset that also has a built in mic.
We have both the 15" and 13" late 2011 Macbook Pros, and they both have this port for in/out, but the 15" also has another input only jack for standard 2-wire (1-channel) cables. I tried my headset from the iPhone on both and get audio in through that mic on both.
I'm not sure if there are cables or adapters out there that will let you plug in your guitar jack (1/4", or 1/8" with adapter) into this multi-axial cable (tri-ax or quad-ax or whatever it is), but I would guess there are options. If not, one could possibly hack an old or unused headset that has a built in mic, with some careful wire stripping and soldering (not recommended for most people though).
There is no excuse for that Apple "Genius" Bar response to this. They should know their product. Apple also sells/includes Garage Band, so they should have included some info about this up front and they should offer a product for audio input. The product is otherwise really stupid and we shouldn't have to buy expensive kits to get decent audio quality. Making customers take all of this effort will drive them away. Ok, end of rant.
I hope this helps.
Edit: Here's a much better description of the connector that I was referring to:
http://en.wikipedia.org/wiki/TRS_connector
...and here is a link to a (rather expensive?) version of an adapter that should work (listing it here as an example, I have no experience with this model, brand, or seller):
http://www.kvconnection.com/product-p/km-iphone-2trs.htm
...and another one they have with a 1/4" input:
http://www.kvconnection.com/product-p/km-iphone-43f35f.htm
We basically seek a 1/8" (3.5 mm) TRRS (Tip Ring Ring Sleeve) to TRS + TRS (or dual TRS, or something like that).
Edit 2: (As I learn more I keep posting) If you care about sound quality for recording, there is an important consideration for impedance matching (
http://www.wired.com/gadgetlab/2010/03/make-it-iphone-guitar-connection-kit/). The more expensive USB devices probably take care of this aspect, and I'm not sure if the built in analog to digital system in the Macbooks have this circuitry.
