Anecdotal experience: the problem wasn't that bad
....for this one happy 2013 Air user, anyway, even before the patch. Score: WiFi access points 4, Air 3. My year-old Apple AirPort Express (naturally), the WiFi at a uni where I was at a conference all last week, and the free "high-speed Internet" WiFi at the hotel where I stayed were all fine. Spent two days at my sister's place in Maine (the US one) with an ancient DSL modem/router combo, and not so happy: leases would be dropped after 2 - 5 minutes.
Obviously that sample isn't large enough to yield any insight into the technical issue(s). The default log entries were spectacularly unhelpful, and I wasn't going to be in range of the suspect router long enough to warrant taking time away from a pitifully short holiday to get more detailed logs.