I use it, and it is the bee knees. Since we started flying premium cabin recently, it has been a breeze. From the time our wheels hit the ground to when we were standing at our next gate took us 30 mins last time we flew internationally. That includes taxiing to the jetway, deplaning, immigration, gathering checked bags for customs, rechecking bags (which was more than a drop off), clearing security again and finally, walking to our gate. Some of that is premium cabin perks rather than global entry...
The biggest advantage is the pre-check program when flying domestically. No line, do not have to remove toiletries, laptop, shoes, sweater, coat etc. Put things on conveyer belt and walk through a metal detector. Oh how sweet it is. Of course the downfall is you never know when you won't be selected for the program, so you can't plan on a 30 second security check and show up late. But, I'd rather be munching on my auntie anne's pretzel rather than standing in a security line.
One trick if paying outright, if you do Nexus, it costs $50 and includes global entry. If you do global entry it costs $100 and includes nexus. A little tip from the TSA agent who did our GE interview. Of course, you need to live near or be visiting the Canadian border. Don't try to make sense of it, just roll with it...
