Originally Posted by Retro Grouch

Chains are one of the least expensive components on your bike. Cassettes are about twice the price of chains. If you let your chain go for too long, it will also wear the cogs in your cassette that you use most often. Then, after you replace the chain, it will skip when you are riding in those cogs.

My recommendation is to replace your chain when it's somewhere between the .75% and 1% wear indicators. If your chain goes past 1% there is a very good chance that you will need a cassette replacement also. I think that running a chain for too long is a poor economy.