Really depends on your climate. Around my area, a good irrigation system will significanty decrease your water usage... and I would gage it as almost manditory if you like lawn (xeriscape is a popular option too) its very dry here through the summer. Built in irrigation allows for better precision and control. If you plan on watering the mature lawn at all, I would still consider in-ground.

Don't know if it's too late, but ...

What are you doing in terms of landscaping? How many zones would you have?

I find that having sprinklers and drip on a timer is invaluable. You don't forget to water when needed, and more importantly, you don't forget that you turned that sprinkler on your hose on and forget to turn it off on time!

I recently upgraded my timer (when it died) to a RainStation and love it. It downloads weather information over WiFi and automatically updates the watering times for me. And you can configure it with a lot more detail than "normal" controllers.

Here is a link that might be useful: Rain Machine