Problem:

Users need a quick and intuitive way to move in and out of large images or canvases in a way that does not conflict with other navigation methods and is easily discoverable. This method can lead to discoverability problems on mobile computers which often lack a (visible) scroll wheel functionality.

Rationale: 

Many zooming implementations use the scrollwheel on your mouse to do zooming.  In fact, this was the wheel's original intended purpose, but it got coopted into scrolling due to lack of ZUIs at the time.  

Variants:

Zoom to point is commonly used for zooming with scroll wheel.  Some implementations do zoom around the center of the image however.  Others zoom around the center of your viewport.

Known Uses:

Seadragon Ajax uses zoom to point.

Ahead.com uses zoom to point.

Hyper-Photos uses zoom around center.

OpenZoom uses zoom to point.

Magic Touch uses zoom to point.

Zoomorama additionally uses overlay cursor for zoom to point, mostly for mobile devices users. (Patent pending).

SimCity 4 uses zoom around center.

MosaicManiac uses zoom to point.

KrPano uses both zoom to point and zoom around center.