Neteller Currency

Weeeeeeee

I want to set up my neteller to use Euro's
I plan to use it exclusively to pay up at € sites
But I have to use it to fund my FT account also ($, obv)
What currency conversion costs am I looking at here? Will there be any other hidden costs?
How do I know which rate Neteller will use?

FWIW, when withdrawing into my bank account, its in another currency which is currently pegged to the dollar at a fixed rate anyway's (therefore, Euro's make me more money)