Had to look to find your question since it wasn't addressed to me.
No, I don't think we're getting hit with DoS's. I don't have a lot of experience with them, but would suspect that connection count and/or CPU utilization would ratchet up quite a bit when one's happening, but they're not. CPU's humming along at about 25% right now, sessions are at about 5k, and neither number seems to really change before IIS shuts down.