This would be a nice feature; I know I would use it. I travel allot and
could keep watch of my home weather and my work weather.
Maybe allow up to 5 locations, or make it completely dynamic and let
people have unlimited locations. Maybe just put a disclaimer with
wording like: More then X amount of locations could drastically
increase load time of your customized home page.
Why just the weather? Allow multiple everything. Let users customize
the news, and add a few different news blocks. Allow multiple Gmail
boxes for different labels (one of them could be the inbox) or