IPv4 to IPv6
It's not likely to be critical for your installation today, but sooner or later it WILL be a factor in your IT plan.
Here is one of the best overview's I've seen on the topic so far:
Ask Ars: How should my organization approach the IPv6 transition?
And if you think you can simply ignore the topic:
Why the IPv4 to IPv6 transition will be ugly
Let us know if you want help with an IPv6 transition plan.