WordPress 2.5 has been released and includes a huge number of changes over the WordPress 2.3 series. The new version is considered to be a major step forward, lots of elements have changed in the interface for example.
Some of the major features in this release include:

faster loading
cleaner interface
integrated gallery and media management
built-in gravatar support
plugin one-click updates

While getting new versions of your plugins, you might want to also check a new interface for your administration, Dashboard Widgets.
Dashboard Widgets — the dashboard home page is now a series of widgets, including ones to show you fun stats about your posting, latest comments, people linking to you, new and popular plugins, and of course WordPress news. You can customize any of the dashboard widgets to show, for example, news from your local paper instead of WP news. Plugins can also hook in, for example the WordPress.com stats widget adds a handy double-wide stats box.
One feature that I like is Few-click plugin upgrades.
Few-click plugin upgrades — if the plugins you use are part of the plugin directory since 2.3 we’ve told you when they …

Here is a simple guide how to change the default size of the thumbnails that WordPress 2.3 creates when you upload an image.
It is actually quite easy to change – it just requires modification of one WordPress file.
From time to time I wonder just how big the image thumbnails are, and occasionally I even ponder how to go about changing that thumbnail size.
The size for the thumbnail creation in WordPress 2.3 could be changed in the /wp-admin/includes/image.php file.
Just open the file and search for:

$max_side = apply_filters(‘wp_thumbnail_max_side_length’,
128, $attachment_id, $file);

and change it to:

$max_side = apply_filters(‘wp_thumbnail_max_side_length’,
256, $attachment_id, $file);

That will double the thumbnail size like mine
Well done and have a great day!