1. Ease of publishing.
2. Discoverability. (Pings weblogs.com or technorati or another ping server).
3. Conversationality. (Trackbacks or as-they-happen referer logs, or now being part of Technorati and other blog search engines).
4. Linkability. (All posts should have permalinks).
5. Syndicatability. (All content should be available in RSS feeds).
+ 1. Commentability (All posts should welcome comments).
By Scoble, via LexBlog.