Start it up, wait for the O2 sensor to heat up and the engine to go into closed-loop mode (aka the RPM will drop), wait about 5 more seconds to see if it's idling smooth, gently drive off, wait for oil temp to hit about 185 F (monitoring with Torque app), drive it like I own it!
I am of the opinion that letting a modern engine idle while cold is bad for it, so I try to minimize the time I spend idling and warm the engine up by driving the car gently.
For the oil temperature, 185 F is just an arbitrary number I picked because that seems to be the first place where the oil temp "plateaus" when I look at my log charts... my oil temp curve starts out as a nearly linear constant rising trend, then it'll stay 185 for about 3 minutes before jumping up to around 200. I don't know why it does that but it's a pretty consistent pattern that I observe in my logs so I have very unscientifically concluded that 185 F must mean it's warm enough for government work.
Also, this:
In all my logs, when the coolant first hits its peak temperature and stabilizes at about 190 F, the oil has only gotten up to 150 F... and that's once the coolant is already fully warmed and the needle is pointing at the second line after C like in this picture here:
[IMG]http://www.ridelust.com/wp-content/uploads/2012/10/DSC_2092.jpg[IMG]
...so for all you guys saying you start driving it hard once it hits the first mark after C (I'm just assuming that's what you mean by 1/4 warmed) just know that your oil is actually still very cold at that point in time.