The spawn rates on mobs (in Dyn-Jeuno at least) are ridiculous. If there's not another group there clearing also, you can easily get over run very very quickly.

I know you can sneak/invis through, but you kill a mob and about 30 seconds later you can expect him to be back. Jeez, tone it down, it's not like billions of people were still doing Dynamis in the first place...we don't need the spawn rate of release day World of Warcraft expansions.