Using it right now...seems to run well and not too resource intensive, no more than FF, anyhow.
One problem I've found is that some images do not appear, just a red cross instead. However, only been fiddling with it for a short while and figure it can be tweaked, etc to resolve the few small issues so far found here.
Generally speaking it is a good browser and is faster than IE6....the full release should prove to be quite something is this beta version is anything to go by.
Shall know more once I've played with it more, but yeah, it seems to have potential and a fair cut above previous IE releases.