Maybe it's been tried, and probably not everyone would use them.
Under the thumbnails, along with the stars, number of views, number of pics, add a line that's the date submitted? It could be a file date or from a database, doesn't have to be super accurate.
And/or maybe a "subscribe" feature where you can select certain favorite members and get some notification when they post a new contri? That would probably be a nightmare to implement.
It seems like Facebook and eBay both do something similar to this subscribe thing.
When a new contri is submitted a flag gets set or it gets added to a table of new contris. Then some nightly batch process goes through the list of subscribers and wherever there's a match with a subscription and a new contri it goes into a temporary table. When its done with that subscriber it kicks out an email or in-house message listing all of them, dumps the temporary table, moves on to the next subscriber. At the end of the run the new contri table gets cleared. There'd be some overlap in timing so you work with a snapshot of the new contri table, contris that come in during the batch wait until the next day's message. Each user has a table of subscriptions with a web form for managing it. I don't know how things work behind the scenes, hopefully it's an SQL database.