I drilled out the original Natural when the first came out. Hadn't planned on using it for a spare ball, but I actually like it for spares better than polyester. Less squirty in the heads, and gives a small but very predictable move coming off fresh strips.
As a strike ball I think urethane, until recently, has been very under utilized, especially by staighter players. As a low rev senior, I find use for it on very wet dry house patterns, and short tournament patterns. Carry can be excellent when you dont try to open up the lane, but instead take advantage of the ability to square up outside.
One interesting side note is the amount of oil that a urethane ball will absorb. I have soaked the oil out of mine at least 3 times and guys are amazed how much it gives up. It may be the result of some resin additives, but I know from experience that even the old blue hammers soaked up oil, we just didnt realize it back then.
