I was a guest recently of a Netjets owner and was very impressed with their service. We were about to board the plane and the pilot noticed what he thought was hydraulic fluid on the ground below the plane. So he instead directed us back to the FBO, since there was another Netjets plane on the ground and ready to go,

Apparently, since the plane had been in the area, they had flown it over to this airport as a hot spare the night before, just in case.

In the end, the fluid was a false alarm, and we took off in our original plane. But the availability of the back-up was impressive.