Above and beyond the numerous bugs and security updates, the new Joomla 2.5.5 release has a good number of new features to help improve your Joomla experience. The first feature is geared toward making Joomla designer's lives a little easier by allowing them to copy templates. If you want to make a complete copy (including lang strings) of a template and rename it, this is now possible in the template manager in Joomla 2.5.5.
Secondly, Joomla 2.5.5 has integrated the terms of service (TOS) in the user registration process and in the overall website. You can enable a clickable link in the user front end registration process for the TOS and when a user clicks on it, an article with the TOS will light box up for the user to see.
The next helpful feature being introduced in Joomla 2.5.5 is the ability to restrict users from changing their username in their user profile and to limit the number of password changes allowed in a given time frame. This will help keep users organized and filter out fishy accounts on your website.
My favorite feature included in this update is a new preview box which appears when you are uploading any new images. This small thumbnail will pop up once you have selected your image for upload, assuring you that you are uploading the correct image.
In an effort to speed up the backend editing on Joomla, they have now added a few helpful buttons in the module manager so you can now "select all", "Clear Selection" and "Toggle Selection".
The last helpful update included in the Joomla 2.5.5 update is a multi-upload feature to help save time when uploading multiple images. You are now allowed to select multiple files from your computer and when uploaded, they will continuously upload in a batch.