[neallewis]

It will vary from charger to charger. I've tried measuring IR figures on difference charger platforms, and the same pack will give different readings on different chargers. You can't therefore use the actual values measured on one pack as good or bad. In theory a lower IR value is better, but I've taken a pack with a value reading of 7-8mOhms one one charger, and it come back with 20-30mOhms on another. The higher value is a consistent measurement on that charger and lead set, not wrong.

Measure your packs and look for consistent figures (or significant changes), not what the actual value is, as it doesn't really matter. Knows what's good and whats not by measuring your known good packs and keeping note of the values.
Some chargers measure the pack as a whole, others measure each cell in the pack, which can be useful in detecting a failed or failing cell.

Edit: Additionally a low reading is a low internal resistance, which is desirable. A higher reading is worse. if you are getting 5-50mOhms measurements on your charger, then i'd not be worried. if they were consistently reading say 8-15mOhms, and then you suddenly got readings of 1Ohm, i'd say it was duff or failing, or very out of balance.
As was mentioned above cycling packs can help with measured IR figures. If a pack has rested for some time, your first charge may give a high(ish) reading, but after a few charge, race/discharge cycles, it will drop to its typical lower value.
Just observe what you normally get, and look for the times when it's off that typical reading.