I have started using a 2820 using g + n, I use a laptop and a desktop connected using N as well as a AP700.
My sons MAC and iphone connected fine when he came to visit and I have got green field mode and also 20/40 channel width set too. I expected those to cause trouble but they did not!

Hmm, this could be what I am seeing with 3.3.4.1

However my problem seems to be that everything is fine, but it all goes ape (and nothing can then connect) as soon as I try and connect from my desktop PC that has a Netgear WN311B 802.11 adapter.

It could be 4 devices, or it could be this partular device that's tripping it all up...

EDIT: Things only stabilize wireless-wise, when I set the router to 11g only