Lama Ole’s answer:
There are different kinds of dreams. Serious dreams are messages from your subconscious, and there you should check it out a bit before talking about it much. With dreams where you see buddhas and bodhisattvas—these are something very special which you should not share so widely.
On the other hand, if you dream of something funny or interesting and it’s not too explosive, then of course you can talk about it. And if you are together with friends and someone shares about a dream with Karmapa, then this is actually a blessing for everybody. Everyone gets something good each time Karmapa is mentioned. Only if Karmapa tells you something in your dream that you think was meant especially for you, then you should keep it to yourself. Everybody who has dreamt about Karmapa can feel this.