First, let's take care of that pesky *of*.

> The documents contain informations of great importance. 

> The intercepted informations were of little merit.

This doesn't speak about the subject, the actual content of the informations but about the informations themselves: *'of questionable value', 'of no interest to me', 'of utmost urgency'*. This is a rather formal, official form. Normally you'd say "important information" or "urgent information", but the *of* form is a well-accepted formal phrasing.

You *might* try to use it to indicate *owner* of the information, but that's really awkward. "The disk contains information of Sony on their newest mp3 player" - but I don't think you'd ever encounter it in real life. "From" or "By" will be much more natural.

Now, the subtle difference between "on" and "about". They are practically identical, with only subtle differences in rare cases. While "on" will be always information directly "on" the subject - the direct data like name, own properties, things relating directly, "about" can relate indirectly.

> I have a new information about Mary: Her boyfriend was yesterday at her flat at 8PM and there was no one there, lights off, door locked, no car.

You wouldn't say *information on Mary* in the above example. That's an indirect information, a hint, something that tells us she wasn't there then, but doesn't tell us anything directly. It sheds some light but it doesn't relate to her directly. Still, in great most cases you can use the two interchangeably.

There's one more case when you use strictly *on*: Dirt. Tools of blackmail. Proofs against given person in investigation. Compromising informations. 

> Finally, we got some compromising information on Fisher. He called a drug dealer yesterday, and we have the call recording implying he wants to buy some drugs.