If you have Windows Vista or Seven and Fallout is installed in "Program Files" you may have problems (editor doesn't see save games, doesn't save changes, etc)..
After you finished editing, click "Save" button under the list of savgames to apply the changes.
2. Miscellaneous information
F1se changes critters in whole game, not single save.
*Editing of inventory is dangerous because information about format is incomplete! (Backup savegames)
*Changing quantity is almost 100% safe. You can set quantity to zero(very bad idea) but why would you?
*The transformation from one item to another - a bit dangerous.
*Creating items - very dangerous.
*If you delete map from "List of *.sav files"(Maps tab), it will return map to its original state next time when you visit it. (When you delete maps from list, you must be in some other location or savegame will be damaged). May be useful to respawn accidentally killed NPC or something like that.
*If you change character stats, better change "Bonus Stats" than "Base Stats". In game stats = base + bonus, but some of base stats are recalculated by game engine at each load. Also some stats have ranges can be seen there:
3. Misc tab. "Bugfixes"
*"Ghost mode" box must always be unchecked. If it is checked, then I bet you are "drawn under objects and scenery and cannot be seen by other critters"
*"Clear combat info" button: If you save in combat, it can corrupt your savegame and you will receive message that game unable to load savegame. Button clears combat info and turns combat mode off. (Very rare bug, I had meet mention about it only on Russian forums)