Twitter - continuous time element

Searching Twitter I notice results are coming up on an hourly basis, leaving off at perhaps one to two days max.

Would it be right to assume then, that to be effective; daily, near fanatical, constant comments are needed to obtain results from this effort?

What happens after a day or so – are your comments available to followers only? Is this communication aspect the one advantage Twitter has over Facebook – where I would have a single company page?

Is it unusual on Twiiter to see a company Twitter Tweeting with a personal Twitter?