Usher relies on Apple's QuickTime technology to display video. If you're tracking movies stored in non-QuickTime formats and using Perian or Flip4Mac WMV to watch these movies in Usher, you may find that the initial import step takes a lot of time—this is particularly true of MKV files. (This isn't true of every format you can watch using Perian and Flip4Mac WMV, just some of them.)

If you're importing a lot of MKV files, you may want to separate the task into smaller batches. By working in batches, you won't save any time, but you will be able to insure that the imported movies are handled correctly, and fix any errors that you find before proceeding to the next batch.