Every manufacturer and your national/local government safety association will have something to say about the life time of your harness.
Take the time to go to the manufacturers webpage to find out how long they say the harness should last. You'll be amazed at how much other incidental info you'll pick up along the way.
I know that everyone can show a harness that is decades old and still in use. Without tearing the harness to destruction you can't know for sure how much strenghth loss is there.
Therrin gives some good points about harness choice.
the trend these days seems to follow the same direction as my Dad observed about womens' swimsuits. The less material the higher the cost. The current offerings of high performance harnesses seem to have less material that the traditional conveyor belt and flat webbing harnesses. Those belt and webbing harnesses do work...at a much lower performance level. Setting value can't be done by comparing prices alone.
There has been a lot of good talk about this new ergo harness called Treeflex over at [hmmm...the name got edited...why is that? dot com. I found this site from a referral from there. Too bad
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could be a good choice too.