Hi,
Thanks for the very thoughtful and detailed feedback here - we love it when folks take the time to do this as it helps us better understand what you like or want
File format support for other filetypes is on the "to do" list (specifically MusicXML, as it's the defacto "all speak" format). Smooth scrolling is also on the "to do" list. You're right that it would make playback on smaller screens much better.
Exporting MIDI - For the muted staves, we have toyed around with an "Options" dialog that would allow exporting only staves that aren't muted. This would require some careful consideration, though, as a "muted" staff is still part of the file. We'll add your vote to the cause
Re. the exported repeat issue, I think all you need to do to make life grand is to be sure to check the "Write out repeats..." box at the bottom of the Export As MIDI File dialog box. Checking that option should export a .mid file that plays back just like the .not file plays in Composer, unless I'm not understanding the problem properly.
I'm glad that you're enjoying Notation Composer, and thanks again for the encouragement and suggestions!
ttfn,
Sherry