I don't have any idea how Twitter sends or stores its "Tweets", nor for how long.
However, I could have a more useful answer to your question of storing personal findings and notes while online. Without being too much of a shill, the Opera Web Browser has this feature called "notes" that is like a small, built-in wordpad that stores your individual notes much like "yellow stickies".
What's more, you can synchronize them to an Opera account so that you have them wherever you have an online connection. And you don't need to store notes to yourself that can be openly-accessed by anyone either. Here's a
link, and yet one
more that help illustrates its ease and functionality.
Sorry if that sounded like too much of a sell for the Opera browser, but it seemed as though you wanted an alternative for Twitter's function of sending/saving text musings.
Hope you give it a try, at least, to see if it serves your purpose in full.