Worst-case scenario: the UEd Goblin wipes the map and burns down your house.

From Unreal Wiki, The Unreal Engine Documentation Site

Something about the grid in UEd.

Things to cover include:

• How to set grid size.
• Why it's best to keep brushes on the grid. See, the Snap to Grid Feature.
• How to make other actors snap to grid

maybe also:

• mention that snap to point seems buggy

[edit] Advanced Grid Options

These are set under UnrealEd Advanced Options.