It's an iPhone only photo sharing lifestream app. Pictures are uploaded directly from your iPhone to your profile where friends can "follow" and stay up to date - sorta like Twitter. You may be wondering why there's a need for yet another photosharing service. Okimok is more like a lifestream. Only the most recent 15 photos are displayed in your stream. Older ones are disgarded. Think of it as a cool way to visually check out what your friends are doing.
Here's my Okimok, follow me!
Have you seen http://www.mynameise.com? They recently launched and redesigned their whole service and are also from Amsterdam, like Okimok. Very cool!