IMHO, they are awesome!!! Need a boat anchor? Paperweight? Something to drop on your enemies feet? It can fill those needs and more. Great for punchlines, too! How are you feeling today....just point at it, it speaks for itself.
In reality, if you had it already, or it was really really cheap, and you weren't looking to make a high revving, high horse engine (think truck) they would work. If you are building something more, find a good stock forged, the balancing will cost the same, and you're starting with a better part. Just my thoughts...