For one of our modules called "node_access.module" (yes, the function and table exist, this is an expansion of it) we wanted an advanced multi-select. My college Wouter has created a pragmatic implementation 1/2 year ago. In the last weeks I finally got the time to refractor it.
Many systems create an advanced multi-select by having two lists one you can select from and the selected list itself. I created two demos with plain html files to show the js functions. Next to a double select list we have the option of a free-input that actually can be a ajax function.
In the first demo we show a simple implementation of jqselect.js with suggestion list and free-text. The second demo is the js part of the node_access module, you can all js and html files of this two demos, its warped in the attach. Notice the suggestion list or free-text (with or without ajax) are options depending on the ids in the html.
The next screencast explains a bit about the functions of the second tutorial where this time also the ajax part works (in demo2 its a simple free-input).
Notice there is no AJAX function in the second tutorial as in the screencast, so some stuff will go wrong with the advanced as any normal free-text has no id. Also my apologies about the layout bug in the screencast, this is correct in the tutorial2 and on the live knosos site.
There are several reasons why we like this node_access method, mostly because there are no limits to the access. Another reason is that research on knowledge sharing we know that closed communities share more than open communities. We try to get some of the benefits of closed communities in an open system. Some examples:
I'm working on a 5.0 release for the modules, will get it in the head asap.