It's nice that there is button in applet's preferences to quickly open site to find out WOEID string .. but can that somehow be changed to autoget it for current location to make applet more .. end-user-ish? :) In addition to working 'out-of-box' it may bring extra bonus of auto-changing for roaming users (maybe worth also add redetect frequency setting). Yes, it may misdetect sometimes requiring manual setting, but one initial preset for all seems to me worse and needs many manual changes for roaming users.
If autodetect will ever be implemented, imho worth to cache few previous locations that were detected or manually set, to be reused when failing to detect current location/it's WOEID for some reason (eg. because of unavailability some externally located site).
1) Imho not worth using IPs from actual wired or wireless interfaces, as those can be behind NAT or proxy, so first with some way find out external IP as seen from outside;
2) There are several tools & sites to get city & country (hmm, probably from whois info?);
3) which then may be used for passing location to
http://edg3.co.uk/snippets/weather-location-codes/ available from pereferences, or another googled up url for WOEID:
http://thale.accu-weather.com/widget/thale/city-find.asp?location= (add city name to it).
I wonder how other weather apps out there handle auto current location issue.