I ran an sl 7 through NG and did about 10 hours of Burg co-op. Made somewhere around 45 humanities, and my host was only invaded 4 times. All 4 had uber weapons (Lightning Shotel, Fire Gargoyle's Halberd). So of course griefers are still there, but so far very few.
The greatest thing though was that my fellow phantoms never used anything stronger than the Drake Sword vs. the engine. I love Burg co-op, but the OP helper phantoms ruin the game for me even more than the griefers, because at least griefers can be killed. (Though I did get a glitch-phantom killed by the Black Knight on purpose once.)