No, you're not missing anything obvious. It's hard! Some people have great ear training to be able to pick out vocal notes.
Add to the normal difficulty that you can have slides from one note to another, and vocals just plain equal difficult!
The way I do it, is I have a pretty fast-responding Korg chromatic tuner sitting at my desk, and I sing each note into it (I find I can match my voice to the vocal pretty well). Then the Korg tells me what note it is (or the note it's near!), then I can play around with the exact note in Reaper.
Be sure to have the option in the MIDI editor where you hear the preview of the note as you move it around or click on it. That really helps you hear if you have the right one.
I have also been experimenting with the ReaTune plugin, which "listens" to an audio track, and outputs what it hears as MIDI notes. It makes a lot of extraneous notes, but I find that it really helps me find the right notes a lot faster than just my ear.
Here is a good document explaining how to use it:
http://www.****os.com/wiki/index.php..._audio_to_midi
Use it on a dry version of your vocal track if you have one.
Good luck!