If we think of a blog as a diary, then a tumblr is similar to a collection of notes about interesting things found on the net or whatever else you might want to share with your friends (links, photos, videos, audio, text messages).
Not everybody has the time or interest to create and maintain a blog, yet with Tumblr anyone can create a simple and beautifully designed personal page to aggregate his digital identity and share content with their friends.
Tumblr can automatically import content from most of the Web 2.0 sharing services you use and show it as a continuous stream on your tumblr. When I shoot a photo with my unlocked iPhone, the iFlickr application automatically uploads it to Flickr and Tumblr shows it on my page, alongside my twitter and blog posts.
Tumblr has just released its 3.0 version with lots of new features and a stunning graphic design which also looks great on the iPhone.
Follow Martin Varsavsky on Twitter: twitter.com/martinvars