I've also been searching for a UWA lens too; currently I have the 14mm pancake, along with the 20mm and 45mm. I use the 14mm most of the time as I prefer wide angles - the 45mm produces lovely bokeh so occasionally mix it up and use that sometimes. The 20mm just doesn't have the 'right' angle for me, though it produces superior images to the 14mm.
I still have the 14-42mm kit lens but never use it as the primes produce sharper images, they are lighter, and cover the focal length.
I rented the Olympus 9-18mm for a week over xmas. It's a nice little lens but decided it's not for me; it's quite annoying having to unlock it before each use (could leave it extended but it doesn't fit as nicely in my camera bag), it also annoyingly rattles around with in it's barrel and as I only used it at the 9mm length paying extra for a zoom doesn't seem worth it. Plus it's not great for low light, which I enjoy.
I bought the Samyang 7.5mm but sent it back the next day. The lens hood was already damaged from the cap, the infinity focus mark was off, and just couldn't justify paying the money for it given these badly designed 'features'. I may have just received a bad copy and tempted to buy another from Amazon given their superior return policy though..
I'm also tempted by the 7-14mm, though I suspect it'll be too big (and expensive) considering I just want it for the 7mm end.
The SLR Magic 12mm f1.6 seems to fit the bill, unfortunately not as wide but it has a nice macro feature and is faster. Also it's hard to buy the SLR Magic in the UK, and manual focus only..
It would be lovely if Panasonic or Olympus introduced at 10mm prime f2 or wider :/