As a result of many new features, new interface and additional changes in the structure of ArcGIS, the ArcGIS 9.4 will be released as ArcGIS 10/X.
GISintersect visited an ESRI conference, and can provide some additional updates on the functionality.
ArcMap 10 will be able to host a ArcCatalog window, easing your access to your files or geodatabases. However, it will still be possible to use ArcCatalog as a stand-alone program.
For geoprocessors, there will be many new tools available, in addition to increased support for Python. Now it is possible to edit maps and layers using Python scripts.
Other interesting news are, New search tool, new editor, raster editing on the fly, python commands in the field calculator. Regarding the attributetable, it is now possible to scroll between attributetables using tabs. This means that you no longer have to minimize attribute windows which is somewhat annoying.
For full details on new functionality, see the list at ESRI: http://www.esri.com/software/arcgis/whats-new/whats-coming.html
According to ESRI dealers, the software will not be available public until after the summer.