There is now an updated preliminary report on the NTSB website:
http://ntsb.gov/ntsb/GenPDF.asp?id=CEN09FA267&rpt=p
The debate about IFR/VFR is resolved:
The flight was being conducted under 14 Code of Federal Regulations Part 91 on an instrument flight rules (IFR) flight plan. Instrument meteorological conditions prevailed at the time of the accident.
But, as mentioned above, still no comment on the cause.