Some folks like to see blogs as a way to have conversations. Blogs reference other blogs; people add comments; trackbacks form back-links to references; all is happy, sweetness, and light.
Twaddle. What we have right now, is a messy prototype. Comments are too prone to comment spam, most people find it hard to understand the concept of trackbacks, and the whole thing is just too damned difficult.
If feeds and aggregation really are going to replace email, it needs to be a whole lot easier to have conversations. Today, conceptualizing, navigating, and adding to a thread is just too hard for 95% of users. (No I didn't do a statistically-clean survey to come up with that number. So sue me.)