Update: It's taken nearly an entire day for sentiment to return to "expected" levels and patterns, and that's not to say that the community has moved on from this news. Far from it. There really haven't been many events that I've seen to have such a dramatic and long-lasting effect on the Twitter community, and it's still happening this very moment. For those who are interested, I've updated the graph below to show a more recent look at sentiment across the day within the UK.
As part of my ongoing research into Twitter sentiment I've always been interested in seeing how people on Twitter react to national and global events. Steve Jobs' recent passing is exactly one kind of these events and has, in my opinion, unsurprisingly triggered one of the largest and most instant changes in sentiment that I've ever seen on Twitter.
In the graph below you can see Twitter sentiment within the UK during the past 60 minutes (top), past 24 hours (middle), and past 7 days (incomplete at the bottom). I think it's quite obvious when something weird happens to the sentiment, but I needed to be sure. After conducting a little research I found out that news about Steve's death broke at around half past midnight in the UK. This timing coincides nearly exactly with the sudden and massive drop in sentiment, which I can only assume means that the two events are connected.
I'm continuing to gather data and I'll be very interested to see how sentiment changes throughout the day as the world wakes up to this sad news.