The current USB + ICP shield supplies 5V from the PC's USB to the TinyDuino. It would be great if there were a jumper to reduce the voltage to 3.3V, which is enough for TinyDuino. That way, it could be used to program TinyDuino inside a circuit with 3.3V components, like most EEPROMs. 

I totally agree. I was wondering why VCC is tied to the USB voltage and not the 3V3 pin of the FTDI adapter, which supplies 3.3v without and additional parts. This would make it much easier to develop tiny shields.
Not I have to add a voltage regulator and a level shifter to a small shield in order to not burn it by the user while having a 3.3V shield attached during the programming cycle.

this would be great.  gets my vote.

Yip this would be cool