I have MacBook Pro at work. It has the glossy glass screen and I'm able to see everybody behind me by just changing the focus of my sight. It's a bit weird.
How do you get used to this mirror/screen?
It is just a matter of time. You do eventually get used to it (I had to). However, the glare will almost always be noticeable. Unfor tunately, this is because of the glass used on the screen. If this is really bothersome, make sure you order the non-glossy screen (another $150). The new retina display MacBook Pro and the newer MacBook Airs have a less glossy screen that the current MacBook Pros.
If it really bothers you now, you may want to look into getting a screen protector. Here is a MacWorld article comparing a couple protectors. I also found one on Amazon. I will note that I have never used on of these.
You could also use something like a 3M privacy filter to give it a bit more of a matte appearance and reduce the glare.
My advice would be to either invest in a matte-style screen protector as others have suggested or to adjust the screen in ways that reduce the glare problem. I usually combat glare problems by increasing brightness or just moving the laptop around until I find a good spot with minimal glare. That said, you do get used to the reflections over time.
I don't think this is something you can get used to if it really irritates you.
The obvious solutions or countermeasures to control reflected light from the glass screen are available:
You could try the easiest of these and hope that in time your eyes learn to focus near so the reflections are out of focus, but unless this irritation is quite new, your eyes may have adapted as much as they can and you will need to look into a different location or exchange the machine for a different display. The Air and Retina MacBook pro are not as reflective as the glassed over displays but also not nearly as anti-reflective as the optional wide-screen anti-glare display that you can configure on some of the 15 inch MacBook Pro models.