The Professional Edition has several features over and above the Standard Edition:

Networked operation
The Professional Edition has an additional Server menu that contains commands to share catalogs with other users and search for clips across catalogs in a central clip database when used with the optional Workgroup or Enterprise Server.
Enhanced searching and filtering
The Professional Edition features a powerful, completely new query dialog, used for both searching within a catalog and when performing remote queries against the workgroup database. Queries can contain any number of terms, be combined with logical OR and AND operations, and include regular expressions. Queries can also be named and saved for future use. There is a new toolbar Filter drop down that can be used to apply a named clip filter to the window. The Professional Edition also features a powerful Search and Replace tool that allows textual replacements to be made across any logging field, including regular expression pattern matching.
Sequence editing
The Professional Edition has support for creating and editing simple sequences, allowing a producer to make a rough cut pre-edit of shots to use and then send an EDL over to the edit suite for finishing, for example.
Unlimited user defined fields
The Professional Edition allows you to create an unlimited number of user-defined fields, compared with the standard number of three. These can be used to record details such as videographer, producer, project, location, and so on. Each field can store up to 64K of text and is fully searchable.
Final Cut Pro integration
The Professional Edition lets you send clips and sequences to and from Final Cut projects complete with metadata and subclip information.
Improved importers and exporters
The Professional Edition supports several additional file formats, including Final Cut Pro, Avid, dpsVelocity, OMFI media files, and XML. MXF support is available as an extra option. You can create image sequences and metaclips, and catalog arbitrary file types such as Word documents or project files as well as media files.
Analog scene detection
The Professional Edition lets you perform automatic scene detection on clips subsequent to them being imported, via a separate Detect Scenes command, and also lets you tune the sensitivity for this operation. This is useful if too many false scene changes are detected, or if scene changes are missed with the default setting.
Timezone adjustments
To allow footage from different cameras, perhaps shot at different locations around the world, to be accurately correlated by date the Professional Edition has a Timezone Adjustment command allows the date to be adjusted based on timezone and camera clock differences.
JKL jog-shuttle keys
The Professional Edition supports the use of standard JKL keys to play media backwards or forwards at different speeds in both the clip details dialog, in the media dialog and when playing full screen.
Additional clip fields
To support these features and more, the Professional Edition supports several additional columns. These include Aux T/C (which displays the user-settable timecode field supported by some DV cameras), GMT Date, Location Date, Location Timezone, Clock Adjustment, Catalog and Catalog Notes.
Customisable proxy settings
In Preferences you can customise the size of proxies and the compression setting used in addition to using one of the presets.
Customisable clip details panel
You can customise which fields are shown in the clip details panel and define new tabs.
Other Professional Edition features
Use the Verbatim Logger to enter log notes while a movie is playing. Create Image sequences and metaclips to treat multiple files as a single clip.