These "junk" accounts get rid of themselves. They are a threat to a certain degree, in that they are a headache and make our forum/community look more low-quality and fragmented than it actually is. I would think that enforcing the rules we have on the books is doing it's part to combat the problem. Junk accounts, alternate accounts and things like that are very difficult to track down without reasonable doubt (if there is any thought put into it), additionally it isn't against the rules. It all becomes rather moot.
We hold these accounts to the same standards as everyone else, as that is the best thing we can do.