On the 12th of February, New Yorkers received the biggest dump of snow the city had every experienced. Looking at the blogging activity around this event we can see a clear peak reflecting that fact. In addition, there is another larger peak. Memory being what it is, I wondered where that other snow fall had hit. However, as you can see from the trend line for New York, when people blog about the weather, they don't seem to explicitly state where it is. People in New York don't say 'it's snowing in New York', they just say 'it's snowing'. Only a small percentage actually provide both the meteorological and geographic information in the text. This means that, yes, knowing where people are located is a key dimension in analysing online data - otherwise, when the aliens land, we won't know where they hell they are.
Actually, the fun way to view this is to consider how one picks up the smaller signal with the intersection of weather and location information automatically.
This trend, showing discussion about earthquakes, suggests that these disasters are blogged about with more geographic information. However, on the one hand the story is international and on the other, the earthquake in question is historical and being discussed in the context of hurrican Katrina.