Hi -
I'm waiting for working drivers (particularly USB) for IBSS mode for long time and was putting my hope on Ralink RT73 as well.
The situation is improving with the mac80211 driver development in the Linux kernel. Recently patches went into compat-wireless that allow to fix the IBSSID with the
iwconfig <interface> ap <cell-id>
command - with some drivers, not all.
However the situation is a little more complex than just fixing the IBSSID, because the drivers/firmware have to be convinced not to perform a IBSS-merge every time the TSF timestamp in a received beacon is a little older. Upon a merge the cards may flush their MAC table - this could happen every few miliseconds - like I have observed with Intel ipw4965 driver. Also TSF clock skews can cause race conditions.
So far ath5k and ath9k seem to work - but the only driver I can really recommend is Madwifi with all patches from Openwrt - vanilla Madwifi is *not* working. The patched Madwifi in Openwrt Kamikaze works perfectly (I'm using mesh with Batman exclusively every day and I can suspend/resume my EEE-PC for weeks and I'm always online ;-)
But Madwifi does not support USB...
Best bet for USB is Zydas, I guess.
cu elektra