There's a 50c transfer fee, or so to send money to a dealer. If you're loading it from your CC then there's a 1.9% charge (at least that's what they quote me in France) and it's instant. If I use my bank's online banking to do a direct bank transfer to MB, it's free, but takes 2-5 working days. You can mail them a cheque too, but that takes 10 working days to clear, but, once again, is free.
If you're pre-loading it like a savings account, you can also use it as a "Hide my watch money from the Missus" account and throw a few quid/bucks/yoyos in there from time to time. When it hits the right amount, drop your favourite dealer a mail.
TTK also now takes MoneyBookers, which is excellent news.