Since you're just starting, can you maybe go beyond what Twitter does in some obvious ways? We've learned a lot about social media in the last few years and you're still agile enough to incorporate all the lessons and make things significantly better.

As an example, my biggest issue with Twitter is the noise, which mostly stems from a single issue: people I follow don't only share interesting things, but they also share a lot of irrelevant stuff such as pictures from family hike. I'm sure this is interesting to some of their personal friends, but not to me. I want to subscribe to that person on a "coding" stream, and leave the "personal" stream alone. People are multi-dimensional beings with many orthogonal interests; Consider giving them multiple stdouts.

Also, I have to say, 140 is often too little :) Will you also force me to write up the occasional longer post on Google+ and then link to it?

This looks nice, I just hope you won't be a Twitter bare bones re-implementation that I have to pay for. Ideology gives you many points, but I'm not certain about just to what degree a sponsored tweet here and there really bothers me.