I'm planning a wordpress website which will use buddyPress, and really important to it will be a list that the user can maintain of their favourite items. Users will need to be able to move the rows up and down to change the ranking of the items, and be able to share their lists. I know this is going to take a fair bit of customization, but I wondered if any WP experts out there had some ideas of how best to create this functionality? would it be better to modify an existing plugin? (not that I can find any), or if not, what kind of JS/PHP coding would be required to create this kind of plugin?
You can do this fairly easily with jQuery / jQuery UI with draggable/droppable-function. You would of course need to have some sort of db-background to store their choices, and write/update the sequence (depending on how many entries these lists will contain, I might suggest not doing this for every re-arrange, but when the user click "save list" or something like that). Reason I suggest jQuery is that it's already available in WP, so you don't have to load extra libraries (although, most JS-libraries are available at load-time, if you choose to implement them).