When I wrote the Hippo CMS evaluation for Open Source Web Content Management in Java, I noted that Hippo really had no presence in North America yet but they were poised to enter the market. Well, it's happening. Hippo BV bought David Sean Taylor's (of Apache Jetspeed fame) company Blue Sunrise. David is now the VP of Engineering and gives Hippo a presence on the West Coast (Bay Area).
I don't know of any North American customers running on Hippo CMS yet. But I wouldn't be surprised if Blue Sunrise customers running on Jetspeed start to move toward Hippo Portal, which is based on Jetspeed.
Hippo BV also relaunched their website under a .com address: www.onehippo.com. When browsing the website I noticed some commas in the URLs that made me suspect that they are running on the upcoming Hippo ECM 1.0 platform (a developer release is due out in April). When I asked CTO Arjé Cahn about it, he told me that they are running the site on Vignette. I hope their North American expansion doesn't make them lose their Dutch sense of humor.