Well I've had it up since the first day it was available; it's been reasonably successful. Hard to tell because this is my slowest time of the year, but it has done better than the 300 x 250 that used to be in those spaces has typically done. Moderate EPCs; it's not the first ad on the page, so other ad units get better paying clicks.
Mine's in the sidebar and only on pages that are long enough to support it; I sure wouldn't put it in with the content or use more than one on a page. And for what it's worth, on all my pages and on all my sites, it ends up being below the fold, after my FB box and search box and some other widgets.
If you're going to use it, play it safe and ease into it.