If you like knowing how tall people are, or how tall anything is really, then you should download Advanced Ruler Pro.
Advanced Ruler Pro is an Android app which features a height ruler that gives you a rough estimate of how tall things are.
To start calculating the tallness of things you'll first need to enter your height, minus a few inches so that your phone's height is more or less equivalent to that of your eye level (i.e. where you'll be holding the phone).
The app measures the distance between you and the tree/building/person. Then you simply aim the crosshairs at the base of the object and then tilt back, until you're pointing at the top. Results are displayed in either Imperial or Metric and can be expressed in units of varying magnitude.
Using the 'distance ruler' setting you can use Advanced Ruler Pro to measure distances between you and a certain point on the floor. There's also a length ruler which displays an augmented reality measuring tape on the screen. This is a bit trickier to use and requires more practice but is useful for measuring windows or anything that you couldn't measure using the height ruler.
We like Advanced Ruler Pro but it would be great if you could save your pictures/measurements to a phone's gallery.
Advanced Ruler Pro is available now from the Android Market for $0.99 (£0.67)