So, you've just set up your camera and you're about to render when you realise you need to zoom in and check something, but you don't want to mess up your camera position. Well now you can zoom in where ever you point your mouse!

Note that this simple method is not persistent - meaning that if you change your viewport and then come back it'll be reset and you'll be zoomed back out again. Richard Yot however, has created an assembly script that ensures your 'zoomed-in-ness' stays put.

Or if you are interested in Richard Yot's assembly that takes this one step further by making it persistent, here's his video explanation here