Is BTC just sitting around in your account, gaining in valuation relative to the euro, considered "profit?"
Is it an issue of intent? If I exchange for investment purposes, it's taxed, but for practical purposes, it's not?
But answering that question is very complex for business, you probably don't need to worry about small gains as a person.
Intent doesn't matter as such - if you do it for 'practical purposes', then you most likely don't realize the gains (don't trade USD->EUR->USD, but do USD->EUR->buy stuff in Europe) or have very small volume (lots USD->lots EUR->go on trip->convert a bit EUR back to USD).
This also appears to not yet apply to Bitcoin, only "recognized" currencies like the Euro.