Whether you deem yourself to be IFR or VFR before receiving your clearance into controlled airspace is a decision you take based primarily on the prevailing weather conditions.
The latest Occurence Reports mentioned an incident in the Scottish TMA where an aircraft had got airborne from an uncontrolled airport with an IFR flight plan and entered class E airspace without a clearance. IIRC the weather was VMC -- I'm not certain if the aircraft entered class D as well, which would change things substantially.
Interesting situation. Is it OK to simply "maintain VFR" in class E until you get a clearance, even though ATC knows of your intention to be IFR? What's standard practice in the US? Do you file a VFR/IFR flight plan for that, or just file IFR?
(Of course it's irrelevant to most of what we do down south in the absence of class E.)