I've been enrolled in both Global Entry and the TSA Pre-Check "Trusted Traveler" programs since they were introduced.
Original enrollment in Global Entry took about two months to be processed (on-line form, then personal interview with fingerprinting, photo, etc, + $100 fee - good for 5 years).
When TSA "Trusted Traveler" came out, I was invited by my airlines frequent flyer program to enroll, and I did so on-line. By entering my "Known Traveler Passenger ID number" from the Global Entry program, it saved me another personal interview, and I was admitted into the program in about 2 days.
In short, they are the greatest thing to happen to travelers since the invention of the wheeled suitcase!
Oh, and my frequent flyer program (United) reimbursed me the $100 Global Entry fee (I believe you have to be Platinum or 1K for the reimbursement).