1.如何设计发布订阅系统

2.如何建立收件箱

3.用户的homepage是聚合的内容，会无限的膨胀

4.unsbuscibe some one，keep the old data in my inbox?

5.one entry is deleted, how to impact on the subsciber's inbox?

6.statndalone comment system

7.use friendfeed’s mysql schema？sdb？cassandra?

8.user's online stat?instant message like?