TBH, Slim, I just think it is too much of a risk, mate. (But then, I'm a risk-averse guy in the extreme, as you well know).
Risky on the financial front for two reasons :
1) The very real danger of the bookie scarpering with the bitcoin. Consider for a moment that Bitcoin transactions are irreversible ........... once the transfer is made there is no chargeback available if fraud is at play. Bitcoin are also untraceable, so your lost Bitcoin are lost to you forever.
2) Bitcoin price fluctuation is highly volatile for the past 6 months. Tonight's rate on BTC-E is 258 Euro. Say you bet 1 Bitcoin tonight on a 4/1 horse; how would you feel if tomorrow's rate has dropped to 220Euro? Your 1,032 euro winnings have suddenly become only 880. That, or worse, can easily happen. So now you have the double whammy of a fair ol' loss of winnings on top of the 25% disadvantage in the odds you took.
I dunno, lad, it's your moolah, your decision. I don't want to put you off what your head and heart might want to do ........... just tread carefully is my tuppenceworth.