i've used Zoop in the past on both motorcycles and cars, with decent results. it does take a bit away from the shine... but does work reasonably well. used it on a set of aluminum/magnesium wheels and was impressed. used it on a polished intake on a V8, and there was some yellowing where there was a lot of heat. from what i hear it can be hit or miss with stuff like that.
now... i just polish my aluminum every once in a while with wadding polish or something like that... sometimes hit it with semichrome. doesn't stay as nice as long as the protected stuff does, but nice enough for me.