I love this post by Woody Windschman:
First, Do No Harm
Use the Product : Don't customize where SharePoint already does what you need.
Do it with Style : Don't build a Master Page when a CSS theme will suffice.
Take the Data View : Don't build a binary web part when a Data View or Content Editor can do the job just as easily.
Master It : When you do need to make major changes to the layout of your pages, customize the Master, but don't throw the baby out with the bath water.
Feature it at Staples : Don't build a Site Definition when you can achieve your goals with Features and Feature Stapling.
The Definition of Success : If you must use a Site Definition, understand the ramifications.
Original post: http://www.thesanitypoint.com/archive/2 … -harm.aspx