I think the old admin panel was easier of use for most things. With the new one introduced in WP 2.5, it takes long time to do some things that were a couple of cliks on 2.3.
This is for posting images:
In WP 2.3, you had all the uploaded pictures all in one way: One click to post each image: 1. Select media center. 2) Select all pictures.
In WP 2.5 Yo have to click many, many times to post each picture: 1. Click button add image, 2. click 'Media Center' 3. Select the page where the picture is. 4. Select the image. 5. REPEAT ALL FOR EACH IMAGE.
And also, this is for those who move widgets frequently (I have 4 sidebars in some sites... and some others have 6 or more sidebars. To move widgets between the different sidebars is really difficult now).
WP 2.3: 1. Drag and drop the widget. 2. Click save changes.
WP 2.5: 1. Select the sidebar. 2. Click Show. 3. Remove the widget. 4. Click Save changes. 5. Select the new sidebar. 6. Add the widget. 7. Put the widget in the correct place. 8. Click save changes.
With this samples, you can see that administering WP 2.5 is so much longer and slower than administering WP 2.3. Because of that losts of users are thinking to go back to WP 2.3.
I cannot understand what caused the new admin panel to be introduced. In my opinion, the panel for WP 2.3 was 1000 times better.