Back in 2009, Matt Cutts from Google wrote on PageRank sculpting saying:

But this may have changed.

Andrey Lipattsev, Search Quality Senior Strategist at Google, answered a question on Google+ which may mean things have changed.

The question was:

In 2009, Matt would have said 1/3rd. But Andrey Lipattsev from Google responded 1/2. He said “1/2 and you can sleep peacefully.”

He did add later (translated via Russian):

Did Google change how they handle flowing PageRank when there are nofollow links on the same page?

Forum discussion at Google+.

Update: Small update on this topic can be read here.