Drill Down Based On Labels
It would be nice if you could choose an option that instead of using the labels to be completely inclusive you can use the labels to be more exclusive. For instance, you could use a label for Windows XP machines and then another label for machines that have Firefox 3.x installed. Instead of having to make a brand new label for windows xp machines with firefox installed you could use both in conjunction to drill down to what you're looking for. This would allow you to create more broad labels that could be used over and over again.