I was on a camping holiday in Wales with my then girlfriend (now wife, woo!), and we knew nothing about it for a few days, as we'd not seen any news, or listened to the radio. After we got home, when we found out, it made sense of some events that had perplexed us:
We were walking through a Welsh town and an American tourist came over to us with urgency, "Are you Americans!?!?!?" When we told him we weren't he walked off. That was probably the day it happened.
We were driving back to Newcastle from Wales and all the cars on the motorway pulled over on to the hard shoulder. We carried on driving on a now super quiet motorway. This was probably a minute or two of silence, but we had no idea.
Learning about it after the event meant that it had less of an effect, and I didn't even see the footage for ages.