I'm no longer a Spike-virgin: I tried my first Shooter (half a can) a couple of days ago. It made my heart pound and I got incredibly hot and sweaty, but it didn't actually enhance my performance; it made me a little light-headed and a bit more uncoordinated than usual.
Had the second half of the can today. (I had poured it into an empty water bottle.) It still tasted great.
My experience this time was better. I had a "bootcamp" style class, and my endurance was definitely up. When it was over I still had energy to spare for stuff like burpees and pull-ups.
I have not yet tried it before heavy lifting; that will be the next experiment.