iPad app for organizing, rating, and noting photos
You can create yourself a Flickr account and upload your pictures to Flickr (as you are already sending the pictures via mail, it should not be an issue). 

On Flickr, you will be able to put your pictures as favorite or not, put description, comments, keywords.
You can arrange them in Sets and Collections and also keep them private so no-one can see them, unless you decide otherwise.  

You have app for this on iPad/iPhone, as well as the website on the Mac or the numerous exiting applications on Mac interfacing with Flickr (Lightroom is also one of them).

The drawback is the limits existing in the free version, but depending on your usage, it could be OK for you.