Here is my take on it.
Would it be useful? It could be a helpful tool if used properly by a fair amount of users. However, I've seen this on other forums I frequent, and it typically seems to get overtaken by a couple of young ones (you know the type.. 12-15, not really matured yet, use it for unimportant things, etc) and anything that was of importance there is washed away, since I see it being.. say 20 lines of chat, unless it would have EVERYTHING in X amount of time. Either way, I would see it being abused more often than not, so I'm of the inclination to say good idea, but would need some parameters to be used properly.