New in version 7.50
Google Chrome support

Internet Explorer 8 Beta 2 support

K-Meleon support

Maxthon support

Firefox 3 Bookmarks Import

Powermarks Import

User Interface Improvements (for example URL ratings can be changed for multiple URLs at once)

Separated automatic retrieval of URL Keywords and Description (Settings | Receive URLs)

Query History

Query "and search" improvements:

When searching for multiple terms, name and keywords of a folder will be taken into consideration for every URL inside.

Example:

You have a folder called "music" with several URLs inside. Some of these URLs have the keyword "software". If you search for "music and software" all of these URLs will be found, even if they don't possess the "music" keyword.
Update information

From 7.x to 7.50:

You can install the new version over 7.x, your settings (including serial number) will remain.