I just switched to Ant Catalog to use it with MediaPortal MyFilms plugin, and I love it.
My only suggestion is that you enable editing of fields in the Grid Display, either in the Grid itself, or by displaying the fields in the window below where the picture appears.
I find the Grid Display is the only way to easily sort my movies by different fields (simply by clicking on the column heading). It also helps me find inconsistencies in my data, but flipping back and forth to the main display is cumbersome. It would be nice to select which fields appear on the Grid, but that is not absolutely necessary.
Although I am missing several fields, the only one I REALLY REALLY miss is the Writer. Now I just add it to the Director field. It is so important for selecting good movies!
I would also like to add my vote for a separate field for the File location (rather than in URL). Right now I use the Source field, but then I have to move the date from the URL field whenever I drag and drop files. A couple of custom fields would be fantastic.
Congrats on a fantastic program!
(some day...)