Okay, technically I didn't tweak it at all. However, there has been a delay in processing viewed messages that would often cause threads you'd already read to show up in your "new replies". That delay has been reduced from 1 minute to 10 seconds.
For those who care about the nitty gritty details, when you read a message, rather than marking that fact in the database immediately, we store it in a queue in memory temporarily. Once a minute, we would grab that queue and process them all. This is much more efficient for the database, but it caused some problems with the "new replies" feature, since messages you'd read up to a minute ago might not have been processed yet. By reducing the delay, we have also reduced the likelihood of that happening. I have plans to eliminate the delay almost entirely in the future, but I'm not there yet.