"As Ortsbo's numbers grow it is highly likely we'll see new users level off"

I don't agree.

1. Fast growing web applications end up eating their competition traffic (Think Facebook vs. MySpace)

2. They get so popular that new users start adapting it. Again, think of how many current Facebook users didn't have a MySpace account (i.e. me).

At some point, the planet does run out of users ... but Ortsbo has a long growth cycle ahead of it if it can maintain a good/reliable service.

"O4O will have to be cutting edge and early to market to stay ahead of the likes of Microsoft."

The track record of Google and Microsoft as successfully creating apps beyond their core strengths is spotty at best. Google has had a number of well-funded and heavily promoted apps fail, so though INT should always look over it's shoulder, it is more likely to be acquired by a major than beaten by a major.