The new UI also highlights Google's video and books stores, so you can rent video or buy books much easier. Google has also said that they have completely rebuilt the Market app, so the entire experience should be faster and more intuitive than before.
An interesting note that Google casually tossed into the preview video for the new Market is that Google is claiming their bookstore has the "largest collection of digital books" on your phone. Google is still claiming over 3 million books in their store, compared to just under 1 million in the Kindle store.
The Android Market update should automatically be pushed to your device (assuming you're running Android 2.2+) over the next couple weeks.
source: Google Mobile Blog