The one initial issue with Tumblr was that it didn’t (and still doesn’t) have built in commenting. That was one of the reasons I didn’t try switch to Tumblr early on (aside from the inability to migrate a blog to Tumblr). I think I have found a role for the various services I use. This is my primary blog, my Tumblr blog is where I share all the stuff I find interesting from Delicious.com, Newsgator and general tidbits on the Web and my Vox blog is where I sporadically blab about personal stuff (well, more personal than this blog).
I would love to know what you think about my Tumblr blog/tumblelog though. I have added Disqus commenting features to it to enable some form of feedback.