Things you can't do anymore
1. You can't when identifying custom panels in your code put in side slashes // what it is. The code most likely then won't work.

2. You can't really have a header anymore from my understanding. It will either cover up the control panel when you edit your profile or just not work correctly. Now if you want a header you'll have to try using a code some what like this one:
#columns{background: url(image goes here) left top no-repeat;position: relative; top: 0px;}
Also if your columns cover the "header" picture up and you don't want it to, try moving them down a bit with this:
#column_1{margin-top: 00px;}
#column_2{margin-top: 00px;}
Note: You'll have to change the "00" to the pixel number you want. The higher the number the farther down you move the columns, and the lower the number the higher up you move the columns.
Intro
Things that changed
New codes
Codes that stayed the same
Multimedia
Things you can't do anymore
Newly Added Codes (Recent Visitors + My Car)