Okay, for all you out there who find World Editor a little laggy.... or alot... here a couple things you can do to reduce this lag...
a) Go to the Window drop down menu in the main window and deselect the Brush List... the brush list is the thing in the bottom left of the main world editor window...not many people uses it and it causes tons of lag!!!
b) If you have Windows XP or 2000, if you have a fast enough computer, you can go to the task manager and change the priority of the World Editor Proccess to above normal or high... i only reccomend you do this if you have a fast enough computer (1.7 ghz at least)
c) Another thing is you can reduce the undo count (how many things you can undo) from 256 to 20 or so. This is in File --> Preferences.
d) Also, odd at is seems, if you have anything overlapping start locations (doodads/units) it can cause a great ammount of lag, so avoid doing this.
e) An obvious thing to do is to close any programs that you don't need running.
f) In Files --> Preferences you can also make it so that on startup, world editor doesn't always start a new map.
g) If your quite knowledgeable about computers, you could increase the ammount of virtual RAM used by World Editor... I'm not going into detail on how to do this.
h) Also, when your not using the Main Window of World Editor, minimize it!
i) If you want to, you can hide units when you're not using them.
j) You can change the particle detail in File --> Preferences... this may cause everything to look like s*** though.