Why is python bug tracker different that ours, they seem to 
be using roundup also. And there is a plus sign to add yourself
to the nosy list. I don't think you can have the a pop-up auto-complete
list as this issue suggests because the list may contain a list of names,
therefore, how can you auto-complete? (I could be completely wrong but just
my thoughts after poking around today.) I'm attaching a screen shot of the
python bug nosy list. Unless you are thinking something along the lines 
of how gmail does auto-complete in the "To:" box with a list of names?

http://docs.python.org/devguide/triaging.html#nosy-list
http://issues.roundup-tracker.org/issue2550741

After clicking on the prior links provided, I came across this message:

jQuery plugin: Autocomplete
Note (2010-06-23): This plugin is deprecated and not developed anymore. Its
successor is part of jQuery UI (http://jqueryui.com/demos/autocomplete/)

In particular, check out "Multiple Cities" at 
http://view.jquery.com/trunk/plugins/autocomplete/demo/

This is actually a bug that would have to get fixed in Roundup.

If you know JavaScript, this would be pretty easy. 
http://docs.jquery.com/Plugins/autocomplete shows the kind of thing that jQuery 
can do with autocomplete.

A few hours' exploration of the Roundup code should let you figure out how to ask 
Roundup to generate a JSON list of the users for the nosy list, and then you can 
query that from a small bit of jQuery.

This  would be great, but keep in mind that it's not a bug in the main OpenHatch 
code, but in Roundup. If you want to hack on it, we will still do our best to 
mentor you!

Just add some sort of JSON / JQuery autocomplete to the nosy text box, I guess.

Because the search popup is a TERRIBLE user interface.