I rarely use Bluetooth and so have it turned off, but it is useful occasionally. The last time I used it was for someone who couldn't sync their Sony Ericsson phone with their PC. Turned on my bluetooth, and on the phone and the two connected instantly, and it was a smooth process updating the phone's software.
Besides mice and keyboards, a common use is headphones. As Slix says, you are not missing out. It is a tool that is there if you need it.
Well I only really use it when my MBA is connected to my ATD. I use the BT to connect to my trackpad and keyboard.
Beside that I don´t really use it for anything else. Sometimes I might use it to connect to my phone to transfer something, but usually I find it to slow. So I either transfer it through wifi or I just go and connect my phone directly with an USB.
I did once use it a bit more to tether with my iPhone, but now my main phone is a Galaxy Note and I use it as a wifi hub. So I don´t need to have bluetooth on to use the mobile internet from my phone.
Also I did use it to autolock my MBP with my iPhone, but it didn´t work so well. Either it didn´t respond properly and wouldn´t lock or open up. Or if anyone really wanted to open my MBP they could get close to me and open it. Heck it was almost like putting a tracker on me for other to find me