1. I am getting weird PHP errors on my pages, what is going on? I have been busy with a lot of these issues and mostly from people who have updated to WordPress 2.5 but did not update any of their plugins at the same time. During the installation process – do not forget to grab the latest version of your plugins as well.
2. My thumbnails are squished – how do I make them look better? WordPress 2.5 allows you to set the size of your thumbnails as well as gives you a “medium” size image option. By default, WordPress uses this option: Crop thumbnail to exact dimensions (normally thumbnails are proportional). If you upload images that are not square – this will really make your thumbnails look squished. I would recommend un-checking this option. (Settings > Miscellaneous)
3. How do I turn on/off Gravatar support? This setting is located at the bottom of the discussion setting page (Settings > Discussion)
4. How can I link my images to a page (attachment) like I did in 2.3? If you want to link your images to a page with a bigger version of the image within your page template, you can do so by selecting “Post URL” in the “Link URL” field when uploading an image with the new media uploader. There is also a new template for this page – image.php. You can find an example template in the default theme.
5. My comments are not visible in the WordPress admin – what can I do to fix this? I have found this to be an issue on some sites with really outdated versions of WordPress. By executing: create index comment_date_gmt on wp_comments(comment_date_gmt); on the WP database – I have found that that usually clears it up. (Thanks to the WordPress forum thread on this)
6. What all changed? If you want a great overview (with a video) check out the WordPress blog post on WordPress 2.5

Hopefully these answers will help you with getting more comfortable with WordPress 2.5. There are a lot of big and small changes to this new version of WordPress and every day I use it – I like it more (and hope you do too).