Well I'm on a first floor and the router is 4 floors above and really wide walls (this is an oooold building), like 15 meters (49ft ?), I have 98% signal strength at day and 100% at night... the link quality is at 100% all day , both %s much better than on my iBook's Airport Card. I must tell that the router is not that good, still I don't have any connection problems.
There are people complaining about the driver stability but you'll find complains about almost anything these days most of them are user's fault. What I can tell is that my only problem is (as you can read at Ralinks forum) that I have a conflict with Photoshop and some USB devices.
I came to this device because my brother surprised me with a SMC wireless device which was a piece of crap (jut don't tell him), I was googling for an Atheros chipset driver which does not exist by the way, and came to Ralink site
(Ralink RT2500 chipsets based wireless 802.11g devices) which stands that some Linksys devices had a RT2500 chipset and they had a Mac driver so I returned the SMC and changed for the Linksys WUSB54G (RT2500 chipset) without knowing if it would work or not... As you can see, it works and I'm happy with it.
The rest of the story is at Ralink's forum whith a How-to make it work.