It is more a platform for sharing quotes, pictures and links we like more than writing long blog posts
It makes sharing quotes so easier - Just select some text on the page and click the share on Tumblr bookmarklet and a quote type of post is shared on tumblr.
It has lovely themes - more stunning themes than in blogger
These two things have made me love it.. Now I use delicious for saving and sharing good links (Delicious automatically posts to twitter). Twitter has a 140 character limit and everything is a url where we have to click to see it, Tumblr simply helps aggregate all the good content in one place.
Just take a look and may be you will also like it very much.
This is my tumblog: http://ananth.tumblr.com/
Check it and let me know your comments.