I'll add to this, while you won't get on then CPU list, United still can see your status and give you a not-zero-but-almost-zero priority for operational upgrades (if economy is oversold but business isn't and all United elites are upgraded).

Happened to me but on Air Canada. This is a very, very rare thing though because you need to count on not having at least 6-24 (depends on plane type) United elites at any level without a companion and economy to legitimately be oversold....but there are some reports out there if you dig through here.