I went in and out of Gibraltar about 6 weeks ago, process took 10 minutes in each direction, no problems whatsoever.
I sort of jumped the queue on the way in, just by splitting lanes until I got to the last traffic light before the Customs post. From that point on I stayed in the lineup. There was no lineup at all when I went out.
The Customs people on both sides (Gib and Spain) were very professional and very polite. Looked at my passport for half a second, waved me through.
Gibraltar itself is much more expensive than Spain for everything other than cigs, gas and alcohol. At least twice the price for food, and three times the price for hotels. I spend a few hours looking around, it was interesting, then I figured I had seen all there was to see, and left.