Everyone now has the option of setting their own default theme.
If you don't like the new theme, you're welcome to go back to the old one! Go to 'Profile', under the 'Modify Profile' heading you will see 'Look and Layout Preferences'.
The first customizable option on that page is 'Current Theme'. Click the word 'change' and select 'Absolute Chaos 2' to go back to the old layout.
Questions? Ask them here.