I know that some of the points here have already been suggested in the past, but since I have recently tried many Photo Album Sharing sites here are a few ideas from this experience :
1. Upload - using drag and drop method into the upload list area. (used i n Yahoo Photo , VERY convenient !)
2. Upload a zipped file and auto-extract in the server side (also VERY useful)
3. auto-created dynamic list for uploaded files. you have a button "add more file" that create for you another dialog for browsing. (Nice and useful)
4. use special add on for both multiple selection or drag & drop. (VERY nice, see example here:
http://www.ofoto.com/HelpUpload.jsp?#easyuploadOne thing that no-one had - is the ability to DOWNLOAD multiple files/pictures. Well, getright browser is the only method I am aware of that can be used with HFS. An option in the template to view the files with "check boxes" near them and have the option to select multiple files - will be a nice add-on too.
I hope this will be of some help and give you useful ideas! Being able to see thumbwheel pictures is also VERY useful if HFS is used for Album sharing .