yes, you should be notified. The policy is also much more black and white now, it is no longer "the top 5% in congested areas" crap. Throttles will be set after reaching 5GB with 4G LTE equipment and 3GB with non 4G LTE equipment.
I've consistently gone over 4GB each month (before this whole 3gb was established) and I was never throttled. I've used wifi at all times (at home) but still pandora all day at work is using up my data since our wifi signal at work is very weak.