Firstly let me compliment you on the excellent CSV import/export function. It was that which made me uninstall the 'other' popular notepad, and install OI Notepad, and all the other great add-ons like Shopping List, Voice Memo, etc. Great job starting the ecosystem around your popular apps.
My problem arises from how successful that CSV import was - with all 200+ personal notes from Outlook now in OI Notepad, I echo some comments I've read previously that this application was simply not designed for large numbers of notes of any form. Categories may prove useful, but only for a relatively small number of notes.
What I consider a major UI improvement is the ability to quickly filter notes based on a couple of keystrokes, exactly the way it works on the Contacts app. So if you typed 'And', all notes with the 'And' in the title in a whole or partial word will be immediately shortlisted. This is the way the notes application works on blackberry as well.
A secondary feature would be the ability to select a sort order, perhaps one of the following: Alpha (increasing), alpha (decreasing), datetime (increasing), datetime(decreasing), category (if that was ever implemented).
Finally, the holy grail is obviously to sync this to Google Docs or similar, but untill that is finally made available by Google, would it be possible to have scheduled backup (by CSV export) to SD card? The key difference between this and the manually initiated funtion you currently have, is that multiple files (perhaps differentiated by datetime) will need to be automatically generated.