I spose I could make having a default amount (or just blank) as a CP option.
However before I release a 1.31 update I want to wait a few days to see if any bugs surface.
But for a quick fix, you just need to edit your XML file and import it again with overwrite selected, or you can just edit the template called 'billspp_main', whatever you feel more comfortable doing.
With either method find
Code:
<input type="text" name="amount" size="6" value="" />
and replace it with
Code:
<input type="text" name="amount" size="6" value="0.00" />