When you start missing a bunch of spares a few weeks in a row.  That's how I usually see it.

My current one is 5 years old.  Hadn't really thought about it but don't see a need to replace unless something happens to it. 

Mark

My fingers/thumb shrank so bad my old spare ball was unusable.

I dug up an old Columbia Vector One and threw a nice glaze on it.  Is nice.

Funny to see a ball that was a hook monster in its day not wrinkle now.

Sorry for a quick hijack, but I saw Bryon Smith was using a Vector 2 as his spare ball in the PBA League telecast last Sunday. First time I thought about those balls in a long time. I used to have the Vector 2, and used a trick drilling on it. Had the fingers and thumb lined up with the arrow on it to make it usable for higher rev players (was supposed to be for low rev players). Ahhh the good ole days, lol.

but on the flip side.. i do not plan on getting rid of this ball anytime soon, just in case i goto a place that had bone dry wood lanes....