I’ve owned the 504HD for several months now and have been enjoying it greatly. I find it to be a great head for DSLR video rigs. See our full review here. The only problem is the 16.5lb weight capacity which makes larger cameras a no-no.
At SXSW, Manfrotto showed off their upcoming 509HD head which has up to a 22lb capacity. It also has an “ABR” feature which detects where your tripod plate needs to be locked down for proper balance. The 509HD head is expected to come in at $899. Expect more details at NAB.