In the mid 1980s, Sweden had a doctor shortage. What they found out was that many doctors went to a half-day of work because the 80% marginal tax meant they were working for next-to-nothing in the afternoon. The doctors took on other hobbies, which their "morning income" allowed to partake.

When the government reduced the marginal rate to 60%, most of those doctors came back to work full days.

With today's offshore accounts, the marginal rate has little impact with those who can afford to live off their interest. They've probably already got legal mechanisms to minimize taxes.