When you are importing you can switch back and forth between a progress window and a log window.
The progress window displays the number of objects to be imported and a progress bar for the percentage already imported at any given time. The bars turn green when complete. When in the progress window, you can switch to the log window by clicking the <Show Log> button.
The log window displays various diagnostic messages related to the import, especially error messages. When in the log window, you can switch back to the progress window by clicking the <Show Progress> button.