Skype started in Denmark, as did Bitbucket, Zendesk, Podio, Unity, SteelSeries, AppHarbor, Tradeshift, Endomondo, Iconfinder, Momondo, TrustPilot and many others (http://starrt.dk/startups).

European software startups that need a huge infusion of capital tend to move some of their business to Silicon Valley while sometimes maintaining a development department back home (e.g., Unity is now headquartered in San Francisco while having its chief development department in Copenhagen, AFAIK).