Mavericks: Zooming images and PDFs in Quick Look is back

In Mac OS X 10.9 Mavericks, the functionality to zoom in and out of PDFs in Quick Look is back: Press and hold the Option key while scrolling with two fingers.

Moreover, the images in Quick Look can be zoomed in to actual size by just pressing the option key.

Unfortunately, it is no longer possible to select text from text files in Quick Look.

Source: Mac OSX Hints