I'm thinking about his doing it / I'm thinking it his doing it ?

[matar0]

( Sorry the title is: I'm thinking about his doing it / I'm thinking of his doing it )

In sentences like:
I'm thinking about/of his committing suicide
I'm thinking about/of them resigning
I'm thinking about/of Jill's having dinner with him

and so on, is there a real difference between the usage of "think about"(to me this is more correct in the vast majority of the cases) and "think of".
Is there any sentence in which should be better using "think of" instead of "think about"?

Thx very much

[Tdol]

Think about involves more thinking to me than think of, and think of is used when asking for or giving an opinion.

[matar0]

Ok, but Is there any sentence(with the structure of the sentence above think of+his/your/their+Verb-ing) in which should be better using "think of" instead of "think about"?

Thx very much