Hi this is a bit late on my part but on the same thread I actually posted the answer which I deleted. AdHoc networks with pis are possible with Ralink based WiFi Adapters I use the RT5370 Ralink Driver which makes Adhocing possible with pis
If you need to refer this here is my query which shows that nl80211
drivers aren't much of help
You can trust me with this since I have spent some amount of time trying to develop ad hoc networks for my work and now I can successfully build a network with the Ralink based Adapters without any hassle. Hope it helps
UPDATE -
with Debian Wheezy 7.10 firmware update the EDIMAX adapters are now adhoc compatible now. This has been tested and checked by me personally today. hence there shouldn't be a problem with infrastructure or ad hoc mode of operation for a variety of wifi adapters now
Although tests on Raspbian Jessie seem to fail!