To resurrect a very old thread - but relevant now with the release of QT 4.6 for Maemo and of Maemo 5 itself ....
I have been using ForecaWeather on my N900 on Maemo 5.

But recently saw the demo version for the QT based "Mobile Weather" app on Extras devel for Maemo 5 - very nice graphics and animation, but it was a demo version and didn't allow saving preferences for locations.

Now recently I saw the "Mobile Weather" app itself (not a demo) - which allows one to save your locations.

But was a bit dissapointed in it incomplete status - like you cant yet change Centigrade to Farenhiet etc - and mostly launching the app is so slow... is this an indicator of QT based apps in general ? I hope now ...