ZDnet has a pretty good article on how European startups find their way (or much more often do not) in the US:

"When you are in the U.S., you have the toughest competition," Liautaud said. "It forces you to improve your products. If you beat the competition in the States, you beat it everywhere."

But in the technology industry, where for so many sectors the U.S. is the main market and thus key to a company's long-term success, European venture capital-backed start-ups that take the plunge most often fail miserably. European VCs reel off myriad reasons for the failure of their portfolio companies to translate technological savvy into business success in the U.S., but common to all the tales of woe is one overriding issue: the paucity of qualified executives able, or willing, to lead the charge.

The alternative, of course, is to retain current management, yet a basic knowledge of the U.S. is still key. "It's a sine qua non," says Laura Morse, Atlas Venture's "human capital" partner, whose job is dedicated to recruiting and retaining managers for portfolio companies. "If you're going to send somebody into the U.S. who is European, the person must have had U.S. experience--minimal would be U.S. education. But to send someone who's never worked or acclimated to the U.S. for a key role is something we wouldn't do."

But while culture is crucial, it goes both ways. "Entrepreneurs check out more at an earlier stage in Europe than they do in the U.S.," 3i's Taylor notes. "They make 30 million pounds on an exit and say, 'Fine, I'll just play golf for the rest of my life.' We have found it more difficult to recycle good management because they get comfortable rather earlier than we would like."

I mostly share the notion in this article. Having brought over two startups lately - 21Publish and Creative Weblogging. Both startups now have considerable revenue in the US. Both have had a though time finding their niche in the US but you why you are trying so hard. The US market is full of opportunities, full of early adopter corporate and private customers, extensive corporate finance options and much less red tape. The basic problem I see that makes most Europeans fail here is the lack of competitiveness imported from Europe, lesser ability to take risks and find customers who are willing to take a risk with a new supplier.

I must say I really enjoy being in the US and for many industries (especially newer ones) it in my opinion the best place to start a business. Other places might excel in some qualities (think public funding in Germany and German infrastructure) but the sum is not to beat fro entrepreneurs in the US.