This rule only applies if you are talking about two seperate activities. Just as likely, you will be talking about two separate components of one compound activity, in which case, you use "is".
"Lying in the shade and reading is fun." (You are not asserting that either activity by itself is fun).
"Singing and playing the guitar is fun."
"Going for a jog and listening to your mp3 player is fun."
In fact, this structure is possibly more common than describing the fun value of two unrelated activities at the same time.
By the way, I think that singing and dancing is fun, given the right atmosphere.
I totally agree with you. I guess if two activities form one concept, it should be treated as singular, while two activities are separate from each other, then plural.
1.Going to nursing home and helping elderly people
is valuable.
2.Helping elderly people and helping orphans
are valuable.
I think this is quite similar to collective noun's number decision.
1. The jury
is making the decision unanimously(same action)
2. The jury
are divided in different opinions.(different actions)
But there seems to be a grey area like the following.
* Going to nursing home to help old people and raising fund for poor kids (is, are) important for young people to realize how valuable such activities are.