I've got a suggestion with regards to the status icons.
The red circle and dot are very nice but the white/yellow/orange seem to be slightly flawed.
White = Read/Nothing New and Yellow = Unread/New content but what is the point of orange?
Orange appears to show up whether something is read or unread simply because a thread has greater than 15 replies. Why does this need an icon when there is an entire column that tells you how many replies are in a thread?
I personally think that things would be more clear if you just had white/yellow read/unread or if you must have a 15+ indicator, only have it replace white icons.
Yellow should always indicate new, it shouldn't be overridden by a redundant status indicator.