Yesterday I wrote a piece that said if I were doing a Twitter clone I'd emulate the Twitter API exactly. Consider that item #0 in my list, which follows.
1. I'd charge users for the service to align the interests of the users with the company producing the service.
2. I wouldn't take venture capital. There's a new law that will allow users to purchase stock in small companies. I'd sell stock to users. If VCs want to buy in at that time, no problem. Level playing field in all ways.
4. I'd open source the software so users would believe #3. No lock-in and no lost user investment if the company is sold, esp because the user's data, all of it, is available to every user, right from the start. See the next item.
5. I'd provide RSS 2.0 feeds for everything. I'd use the microblog namespace extensions, esp fully implementing the archive element. A feed for every user. A feed for every user's favorites. A feed for each hashtag.
6. Allow a user to be a feed. They'd have to pay for the service and no one would have to follow the feed. This allows users to create flows that can appear on more than one network. Super important for users who see their stream as a product.
11. Block with timeout.
12. More ideas in this post from 2010.