user26800: Bitstamp allows deposits/withdrawals using SEPA (EUR only), but all traidings are done using USD. It is nowhere described what exchange rate is used when doing these deposits/withdrawals.
There are some indications that amount of money lost in conversion may be significant:

The order book only offers bitcoin-dollar trading so conversion fees apply on deposits and withdrawals (the conversion spread can be queried by API). [1]
Bitstamp has an EUR bank account in Slovenia to which I deposited euros, then it converted to USD. Then it converted the EUR deposit to USD but I checked the daily EURUSD forex range and Bitstamp converted my EUR to USD at a rate worse even the worst rate in the 24-hour daily range; I have to say, clever: another small profit source for them. [2]

Does anybody know how big the EUR/USD spread at bitstamp really is? Is it significant?
[1] http://blog.kraken.com/post/97016109057/what-does-it-really-cost-to-buy-and-sell-bitcoins
[2] https://bitcointalk.org/index.php?topic=825459.0

user27892: I believe the EUR / USD conversions are preformed by the bank with which Bitstamp works. They have conversion rates which don't appear to be market-driven, but are set to a fixed rate that includes the bank's fees.
The exchange rates link provided on the website leads here:
http://www.raiffeisen.si/pripomocki/menjalniski-tecaj/

26800: <p>Bitstamp allows deposits/withdrawals using SEPA (EUR only), but all traidings are done using USD. It is nowhere described what exchange rate is used when doing these deposits/withdrawals.</p>

<p>There are some indications that amount of money lost in conversion may be significant:</p>

<ul>
<li>The order book only offers bitcoin-dollar trading so conversion fees apply on deposits and withdrawals (the conversion spread can be queried by API). [1]</li>
<li>Bitstamp has an EUR bank account in Slovenia to which I deposited euros, then it converted to USD. Then it converted the EUR deposit to USD but I checked the daily EURUSD forex range and Bitstamp converted my EUR to USD at a rate worse even the worst rate in the 24-hour daily range; I have to say, clever: another small profit source for them. [2]</li>
</ul>

<p><strong>Does anybody know how big the EUR/USD spread at bitstamp really is? Is it significant?</strong></p>

<p>[1] <a href="http://blog.kraken.com/post/97016109057/what-does-it-really-cost-to-buy-and-sell-bitcoins" rel="nofollow">http://blog.kraken.com/post/97016109057/what-does-it-really-cost-to-buy-and-sell-bitcoins</a></p>

<p>[2] <a href="https://bitcointalk.org/index.php?topic=825459.0" rel="nofollow">https://bitcointalk.org/index.php?topic=825459.0</a></p>
 27892: <p>I believe the EUR / USD conversions are preformed by the bank with which Bitstamp works. They have conversion rates which don't appear to be market-driven, but are set to a fixed rate that includes the bank's fees.</p>

<p>The exchange rates link provided on the website leads here:
<a href="http://www.raiffeisen.si/pripomocki/menjalniski-tecaj/" rel="nofollow">http://www.raiffeisen.si/pripomocki/menjalniski-tecaj/</a></p>
