Though I haven't had my hands on one, I'm guessing it is visibly slimmer and lighter, and it also carries the extra ports for viewing on a different screen. You also can't use the original PSP remote with this redesign. They also moved the WLAN switch.
http://www.engadget.com/2007/07/16/sonys-new-psp-gets-a-proper-shakedown-for-new-features/
So, they made small revisions to the shell of the PSP. But, I will agree, I was hoping for a newer look. This is a lot closer to the original than I like.
twesterm - I believe it's supposed to have longer battery life, up to 10hrs. Let me see if I can drag up the article.
Edit: Here it is - http://www.dailytech.com/PSP+Slim+Has+More+RAM+up+to+10+Hour+Battery+Life/article8034.htm
Threads of Interest:
The Movie Thread: http://www.vgchartz.com/forum/thread.php?id=6880
The Crow Eating Thread: http://www.vgchartz.com/forum/thread.php?start=0&id=3886
The Betting Thread: http://www.vgchartz.com/forum/thread.php?start=0&id=7104
Custom GIFs Thread: http://www.vgchartz.com/forum/thread.php?id=18963
The Greatest Game Ever Conceived On Any Platform
Tag: "I have tasted Obi-Wan's bitter tears"