UnrealEd Advanced Options

Holds the advanced properties for UnrealEd, and also many that affect the game itself. To open this from the Editor do:

UnrealEd Main Menu → View → Advanced Options
or type "preferences" in the UnrealEd console or in the game

Of interest to mappers is the "Editor" group of properties.

This allows funky stuff like strange grid settings and other weird options...

Properties

Editor → Advanced

AlwaysShowTerrain: ?
AutoSave: see below
EditPackages: array showing what's loaded ... no idea if messing with this is a) dangerous or b) has any effect
FovAngleDegrees: ?
GameCommandLine: "log"
GodMode
LoadEntirePackageWhenSaving
ShowIntWarnings
UseActorRotationGizmo: no idea
UseAxisIndicator: controls appearance of those little x-y-z axes in the UnrealEd Viewports.
UseSizingBox: ?

AutoSave

Autosave settings are under the Editor → Advanced section.

AutoSave: set to True to enable AutoSave
AutoSaveTimeMinutes: time between saves

Tarquin: found these on both FAQ and Tip pages.

While in UnrealEd, do UnrealEd Main Menu → View → Advanced Options. You should get a new window containing several sections. Open the Editor section and in there open the Advanced subsection. Now set the AutoSave properties to true and adjust the AutoSaveTimeMinutes to whatever you think is best. Now UnrealEd should autosave your current map every x minutes. I know a lot of people you have lost a lot of work because of an editor-crash and they didn't save their map.

Do UnrealEd Main Menu → View → Advanced Options. You should get a new window containing several sections. Open the "Editor"-section and in there open the "Advanced"-subsection. Now set the "AutoSave"-properties to true and adjust the "AutoSaveTimeMinutes" to whatever you think is best. Now UnrealED should autosave your current map every x minutes. I know a lot of people you have lost a lot of work because of an editor-crash and they didn't save their map.

Editor → Colours

Global brush colours can be set somewhere around here too.

Editor → Grid

It's perfectly possible to:

Set the grid to a number that isn't a power of 2, though inadvisable as powers of 2 are optimal for clean BSP.
Set the grid to different sizes in different axes, eg 16x16 in top view, and 64 along the z-axis.
Set the grid to fractional sizes, eg 0.5.

Editor → Rotation Grid

The rotational grid makes rotating objects in the interface rotate in discreet increments.

RotGridEnabled: Whether the rotational grid is active or not – you can set this in the Console bar too.
RotGridSize: the settings for the grid. The grid is set separately for the pitch, roll and yaw. The default value is 1024 unreal units, which is 64 steps per circle, each of 5.625 degrees. You can use any number, though powers of 2 are best (just like the linear grid); see unreal unit for suggestions.