I was reading the notification emails thread, as I too would like to be able to inform my audience of updates to the gallery, however I'm starting to think about this as two different features.
So the first email feature is the one discussed already - admin notified about uploads, mass emails to registered users etc.
The new feature I'm proposing is to allow anonymous (or registered) users to simply add themselves to a sort of "mailing list" for one or more galleries on the site. This way, casual browsers (who usually don't want to register) can just submit their email address into a simple form that adds them to a mailing list database for each gallery. Now the owner of the gallery can broadcast an email to his "audience" whenever something of interest occurs.
Of course, you chaps being all clever and all, will be able to think up a number of clever ways to make this feature work better than I explained it, automatic & configurable options, etc.
But wouldn't it be cool to know who or how many people are interested in your photo album? Personally I run a simple site that shares photos of the kids for my family, so all I want to do is broadcast an email to them all everytime I add some more piccies - about once a month or so.
Also, from a personal point of view, I've seen quite a lot of galleries where some photographer takes photos I really like, so I'd definately be inclined to leave my email address, and revisit their site as new photos get added.
We shouldn't under estimate how off-putting "proper" registration can be, all that login/logout stuff, and remembering passwords has a very offputting effect on any visitors who have limited or passing interest in a site.
I hope I made a good case there anyway!

Keep up the good work. I'm gonna study the source code for a while I think, and see if I can help out in some way...