This depends on your country. For example, in the UK, the Payment Services Regulation 2009 makes no difference between credit and debit cards with respect to a payer's liability. In either case, your liability is limited to 50 pounds (unless you acted grossly negligent, intentionally, or fraudulently), regardless of the type of card used.

This is largely a consequence of article 60 and 61 of EU directive 2007/64/EC [1] (some countries have been lagging behind in implementing the directive, though, so don't expect it to be the law everywhere in Europe).

[1] http://eur-lex.europa.eu/LexUriServ/LexUriServ.do?uri=OJ:L:2...