Jesper - I once read that the nickel test proves you have a nickel and a saw, but not much else.
It's a fun conversation piece but isn't a very scientific test....for starters, not all nickels are a uniform thickness, and not all have nice square edges. There are several other variables too...where you place the nickel, the floor, air flow from the blade, brief regeneration shimmy on shutdown, etc.
If the saw feels smooth and cuts well, I wouldn't worry about it, but if there's noticeable vibration that shouldn't be there, check your belt, belt alignment, pulleys, arbor, motor shaft, blade, etc. Try to isolate each of those components until you have a culprit. There are a finite number of things at can be.
Edit: As I sat here drinking my morning coffee, I was trying to think of some useful descriptors that would help you know what's normal and not normal vibration. I don't normally condone setting coffee cups on cast iron surfaces, but I went out and started and stopped my saw with a full cup of coffee sitting on top.....nearly no visible ripples until well after shutdown, and even those were pretty small. Still not overly scientific but possibly more repeatable than a nickel test.