Also: 24h time with no timezones.
People generally live their lives within the local sphere. There is a lot said in the phase "My plane lands at Narita at 13:00/1PM" that isn't said in the phrase "My plane lands at Narita at 05:00 GMT".
With the first, I know that the locals are just finishing lunch, it's likely to be the warmest part of the day, and that it'll be busy getting to the hotel, but everything should be open.
Converting everyone to GMT means that every time you leave your region, you need to figure out what time customary activities take place - and you need to do this for every single different place you visit.
Standardized GMT doesn't work unless you are a hermit with no friends or need for communication.
If I'm in New York following the nuclear crisis in Japan, it's probably more important for me to know that the next news conference is two hours from now than that it's in "the morning" there. If I'm planning a meeting I certainly want to know the absolute time it's occurring, and only care about the relative time depending on how courteous I am.
I'm not saying we should stop caring about working hours and daylight hours in various places. I'm just saying that those vary wildly and are dynamic, and we should reflect that in our concept of "time".
But then, I'm a nerd.
India is +5:30, Nepal is +5:45, California observes DST but Arizona doesn't... the EU does, but they start and end DST a week before the US...
It's ridiculous.
The initial gut reaction against this is that people would hate waking up at 18:00 and going home at 8:00, but I think people would get used to this pretty quickly. After all, we do this twice a year as it is.
There is also Namibia which used to lose hours in daylight savings time and Bangladesh which had dst in 2009 then dropped it, this makes historical time calculations tricky.