Yes, if you want to be able to see rep notes you have sent you would need to save them in a text file or something.
There is one cool trick that not too many people know about - which is you can see old rep notes that you have received on a post even after they scroll off your User CP. If you go to an old post of yours and click on the Rep icon (like you were going to leave yourself a rep note - fortunately the system doesn't allow you to talk to yourself) a little window will pop up and show the Thanks and old rep notes. The only problem is that it won't show who thanked or left you the rep note, but it is still kinda fun to see the old notes sometimes!
