Present Perfect is used to talk about something that happened in the past but has consequences in the present. It is always connected with now. The action in the past has a result now, for example: 1)Where's your key? I don't know. I have lost it.( I haven't got it now) 2) Is Sally here? No, she has gone out. (she is out now) We also use present perfect to give new information or to announce something that happened recently. Present Perfect Continuous is used to describe an activity that has recently stopped or just stopped, or is still happening(see example 3). For example: 1) You are out of breath. Have you been running? ( you can compare it with past perfect continuous: You were out of breath. Had you been running? ) 2) Paul is very tired. He has been working very hard. (he's tired now) 3) It's raining now. It began raining two hours ago and it is still raining. How long has it been raining? It has been raining for two hours.

Yes, you're right, it's not completely clear when you should use one or another. It seems that in general you can use both tenses indistinctly, without running the risk to be misunderstood. However, if you want to emphasize an action that it's still going on, you should use the present perfect continuous. For further explanations: http://www.englishpage.com/verbpage/presentperfectcontinuous.html http://www.englishpage.com/verbpage/presentperfect.html

North American usage may also have a different sent of time from the British. I would never write "I have lost it". I might write "I must have lost it" or "I may have lost it". WIthout the other verb forms I would simply write that I lost it. I would also never have written "she has gone out". I would write that "she left". The only time I would ever write "had been running" is as part of a relative clause. I had been running so I didn't see the bicyclist. It had been raining for two hours when the rain changed to snow. Notice that the second clause in the past so the first must be further back in time.