Navigating

2D View

Panning can be done by clicking the MMB and dragging.

Zooming can be done by scrolling Wheel up or down. Also, as in the 3D View, you can use NumpadPlus or NumpadMinus to zoom.

View Menu

Also see Navigating in the Image editor.

UV Local View

Displays only the UV faces that are assigned to the currently displayed image.

Display Other Objects

Displays the UVs of selected objects (Object Mode) in the background.

Display Texture Paint UVs

Hides the UVs in Paint Mode.

Frame Selected

Change view so that all selected uv vertices are visible.