One thing ever Gmail user loves is the conversation view. However, one painful experience with the conversation view is the "Mark as Unread" feature which used to mark the entire conversation as unread, which means that you had to figure out exactly which was the first unread post, the next time you opened up the conversation again.
This has always been a painful experience especially if you have ten or more emails as part of the conversation.
Gmail has finally fixed this after being so many years in the "beta".
Now if you’re reading a conversation that had unread messages when you opened it and you mark it unread, Gmail will only mark those messages that were unread when you opened the conversation in the first place.
This is a very very welcome change. I do hope they get this implemented across all the versions, i.e. the new UI, the Older Version and the HTML interface, as well as on my mobile.