We've got Moodle 2.4 ... When we had WebCT, I'd quite often use the ability to search the students & find those not in a group - however, it seems that it's not possible to do it in Moodle.
The nearest I get is to look at the Enrolled users list, and look down the group column, to see who's not in a group. As that column isn't sortable, I can't use it to get them all at the end/beginning, and creating of groups doesn't let you find those not in a group. (I appreciate that when groupings are in use, it's possible that a student may be in a group in the "classwork" grouping, but not in a group in the "homework" grouping - so it would probably be necessary to include the grouping as well as the group.
Is there a plugin for it that I've yet to find?