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If you work on a network with mostly Cisco equipment, there is a good chance you've configured EIGRP or at least seen it configured. The most typical setup would be an RFC 1918 address range (such as 10.0.0.0) as the network, and a the dreaded auto-summary disabled. Most small to medium sized pure-Cisco shops don't use redistribution or modify the K values unless they have some well defined requirements that call for it. That said, here's an example of a fairly typical EIGRP configuration:

router eigrp 100
network 10.0.0.0
no auto-summary

If this is similar to your configuration, Cisco wants to make things "easier" for you. Since nearly everyone disables auto-summary, they went ahead and started disabling it by default. Here is an excerpt from their command reference guide:

 Cisco IOS Release 15.0(1)M, 12.2(33)SRE, 12.2(33)XNE, Cisco IOS XE
Release 2.5, Cisco IOS Release 12.2(33)SXI4 and Later Releases

The behavior of this command is disabled by default (the software sends
subprefix routing information across classful network boundaries). 

The key take away here is that almost all, if not all, versions of 15, and the newest versions of 12.2(33) (primarily used in IOS switches - i.e. 6500's) now have auto summary disabled by default. This means all IOS devices running 15 code will not have the "no auto-summary" statement in their running-configs because it's already there. So, when you start rolling out new versions of code, expect to see your EIGRP config change to something that looks similar to this:

router eigrp 100
network 10.0.0.0

Thank you Cisco, for making our lives more complicated easier.

Here's a link to Cisco's EIGRP Command Reference if you want to read up on the other command references.