not necessarily~~ but if you want some paid apps for customization, then you need to root to access paid market.

i need FolderOrganizer for my customization so i rooted!

other stuffs are just free apps.

Most customization no need root access, except:

• Notification bar.
  
• MOD apps by user. (unless the user developed the apps installable, no need ADB push, or you personally take the MOD apps and make it installable)
  
• Paid apps - as currently Malaysia not support market paid apps, and Market Access or Market Enable needs root access.
  

** Which means, without root you still can customize as nice as it is.
Even though I personally can't stand on the default white notification bar, this is truely ugly for me, ops!