Give this a try for user feedback: zotero.uservoice.com
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1. I think the fact that user requests are awkward and take some time to research isn't necessarily bad. I'd argue that in most cases an informed request requires insights in what exactly is possible, what has been discussed and possibly rejected already already etc. There are much more requests than resources - the economist in my nick says that increasing the "price" of requests is the correct market solution ;-).
2. Along with bdarcus I think that's not quite right. Users input isn't ignored - and there are in fact many examples of user input leading to new features or changes - but for the reasons bdarcus states, some notion of (perceived) user democracy - votes, +1s, most comments etc. - isn't used to determine dev priorities. Also, as noksagt points out above and your comment about duplicates confirms, a company like Mendeley with a more elaborate feature request system, more money and more staff struggles to meet those demands, too.
And note that developers here refers to the paid folks at GMU - there is always the option for outside developers and there are a whole bunch of examples of that type of involvement with fruitful results - from mrronko's quick look plugin to the new CSL to the improved translator dev documentation etc.
3. agree with that - within the current technical framework we could just set up wiki pages for that, but I wonder if it wouldn't be possible to integrate that more tightly with the forum. Maybe fcheslak could chime in?