Never bought ammo from them, but have bought gun parts, detachable magazines, and similar stuff. Good folks, good prices, no problems at all with my orders.
Lately, I have heard they are REALLY busy, due to some great sale prices (as you mentioned), and also increased demand for AR and other gun-related stuff in general. This has resulted in some complaints that I've heard on other discussion boards about slow shipping/order processing times, but they do have a notice right on the front page of their site that says:
** Notice: Due to the popularity of the Free Shipping Event we are experiencing shipment delays **
** Please allow up to 5 business days for your order to ship **
so it's not like they aren't warning folks about it. My experiences with them have been great in every case, but obviously, I can't guarantee that for everyone.