Prompted by a blog post by Ψ*Ψ which referred to a reddit-style voting system for papers, and based on the excellent "Stack It!" feature of Ohloh, I've implemented a Stack It for journal papers using Greasemonkey:
All you need is an account at Connotea. The first time it runs on a journal web page, it asks for your Connotea username and password - this will be remembered until you close the browser. To stack your favourite papers, just click "Stack It!". To unstack, you'll have to log into Connotea. The tag "stackit" is used for all stacked papers.
It should be possible to identify other people with similar stacks to yourself, and see what else they have stacked (Ohloh can do this). Also, you could have an RSS feed to what people are stacking recently, or you could have a list of the most popular JACS articles in the last month.