It is good to use banks as an obstruction with their high HP, but I wouldn't make a wall with it. The problem is that you force yourself backwards and lock yourself up. If you beating someone for example and he's retreating you want to chase him down but that's more difficult with a wall (of buildings) in your way.
Or if your opponent has his army just outside your base waiting it's always nice to use the superior range of your skirms to fire a volley and immediately retreat. You can repeat this a few times so that your opponent has lost some units before the actual battle starts. If you have that many buildings in the way, you are screwing your own pathfinding.
You can play defensive with the Dutch and give up map control, but at one point you need to take map control back, most likely when your resources near your base are gone.
Also I would never put my barracks in front of my towncenter. This is the first building the opponent wants to attack and you've helped him big time to put him front. If you play defensive always put your barracks just behind your TC.
EDIT: Wow, I forgot about towers. Two/three towers can help you defend a lot. Together with TC fire it helps to kill that nasty cav which could destroy all of you skirms or raid you to death. Place the towers not to far away from your TC and each other so that enemy's units get shot by more than one tower. And of course try to cover some resources with it.
"There must be some way out of here," said the joker to the thief
[TΣ]_Ha_Luke_331
"All murderers are punished unless they kill in large numbers and to the sound of trumpets." -Voltaire
"A good decision is based on knowledge and not on numbers. " - Plato [This message has been edited by Ha_Luke (edited 02-07-2009 @ 05:06 AM).]