Just an addition to comment #56:
I upgraded to the latest 10.03.1 RC (r24038) of OpenWRT (running on a Netgear WNDR3700 router) and changed the wireless regulatory settings according to these instructions (setting the country code to 'SE' since I live in Sweden):
After that I tried enabling N-support again and after 2 days I still have not experienced any problems. I have tried both 2.4 and 5 GHz radio.
Also, I had some trouble with my Asus Eee (featuring an Atheros chipset) dropping wireless connections but that also works like a charm after my upgrade.
I don't know if it is the upgrade to 10.03.1 r24038 or the Wireless Regulatory patch that fixed my problems, but I would advice others to also check the settings/software in their routers.