I have been using the Notes to track maintenance and repair on my vehicles. I think it would be a nice feature to be able to view only the Notes (without the fuel-ups).
I think it could be accommodated fairly easily with a link "View All Notes" similar to the "View All Fuel-ups" link that is already present at the bottom of the Logbook section. That link could bring up a similar page, but with the entries filtered to only include the Notes.
After Fuelly was launched, I opted out of keeping Excel maintenance logs because as you have found, it is ten times easier to just log it as a note in Fuelly, along with the date and mileage, and it will print out with any export.
The trick to easy viewing is to tag all of your notes with a keyword when you enter them. I use the tag "maintenance." Now you can go to "View All Fuel-Ups" and find a "maintenance" tag and click on it. It will only show you notes or fuel-ups with that tag.