In the first pair, there would be no significant difference in meaning. The two are equally common in everyday speech. In the second pair, only the continuous tense would be correct. We use this form to talk about the duration of a continuous activity which is either still going on, or has only just finished. We would understand you if you used the present perfect simple, but a native speaker would be unlikely to use it. The continuous tense focuses the length of the activity, whereas the simple tense focuses on the fact or the result of doing this. Look at these examples: I've been baking all morning. I've baked 3 cakes.