Sets the size of the preview thumbnails present in, for example, the Layers, Channels & Paths dialog.
Setting the size to "None" will disable the preview function.
Will affect the size of the Navigation Window present from the bottom right corner of the image window or as right-click View Nav Window
Sets the number of previously opened or saved documents that you can directly access from the Toolbox File menu.
In the ToolBox there is an area displaying the currently active brush, pattern, and gradient. If you don't want the area to be present in the ToolBox you can disable it here.
Enables or disables tool tips in The GIMP.
Enables or disables the Shift-F1 method of enabling context sensitive help. It can sometimes interfere with the window manager. You can still access the context help in the Toolbox Help menu.
Lets you choose which HTML browser The GIMP uses for displaying it's help files: its internal one or your web browser.
Let's you choose whether to activate the pixel-by-pixel mode by default or not.
Enables and disables window resize on zoom. Normally when you zoom, the window size will not be affected. If you enable this function, the size of the window will be adjusted to fit the size of the image when you zoom in or out. Zooming in will enlarge the window and zooming out will shrink the window.
Controls whether you want to show the rulers or not by default.
Controls whether you want to show the statusbar or not by default.
When you make a selection in GIMP there will be a "blinking" boundary for the selection. This "blinking" boundary is referred to as marching ants. This option controls how fast the ants will march.
Sets the window title of the image window. The default custom value is reasonably sane, but you are able to choose from Standard, Show zoom percentage, Show zoom ratio, Show reversed zoom ratio, and Custom. To build a custom image title, you can use some macros along with ordinary characters.
Table 12-1. Title Format Codes
|%%||literal percent sign|
|%f||bare filename, or "Untitled"|
|%F||full path to file|
|%p||PDB image id|
|%i||view instance number|
|%t||image type (RGB, indexed, grayscale)|
|%z||zoom factor as a percentage|
|%s||source scale factor|
|%d||destination scale factor|
|%D*||expands to * if the image is dirty (modified)|
Pointer Movement Feedback
When you are drawing in GIMP, GIMP will not catch your pointer every moment. Instead GIMP catches it at a certain time interval. This means if you draw a circle very fast GIMP will not draw a circle but lines between each pointer grab. However if you turn on Perfect-but-slow Pointer Tracking, GIMP will record every single movement and make a perfect circe even if you draw it very fast. You will, however, not be able to draw in real time instead that drawing will "played" with a time delay since you "recorded" every movement. 
Normally when you, for example, paint with some tool, you will have a little image of the tool as the cursor. If you disable cursor updating, the cursor will always be a little pencil even if you change tools. I.e. the cursor will always be the same shape as the last tool you used before you disabled updating.
Let's you choose between three different mouse pointer looks, i.e. just the toolsymbol, the toolsymbol together with a crosshair and simply the crosshair.
Normally when you paint in GIMP, you set the opacity and paint mode in the Brush Selection dialog. If you enable "Use Global Paint Options" you will have the opportunity to set both Opacity and Paint Mode separately for each tool (the Tool Options dialog will change and you will have new controls for Opacity and Paint Mode).
Finding Contiguous Regions
Here you can choose the default threshold for all tools which is a measure for the precision of filling and masking tools.
Well this is not exactly what happens but it makes it easier to explain it this way.