This new and important paper (scroll to p.29) has lots of useful information:
...the average profits per partner in the top 50, top 100, and top 200 U.S. law firms in 2004, respectively, were $1.26, $1.01 and $0.83 million. These averages are the averages of the average profit per partner for each firm. The medians of the averages are lower, at $1.08, $0.86 and $0.67 million. These profits accrued to, respectively, 11,034, 17,861, and 26,755 partners. Average profits per partner exceed $2 million for 9 firms; they are at least $0.5 million for 93 of the top 100 firms, and 152 of the top 200 firms...Based on these distributions, we estimate that 14,351 of the 17,861 partners in the Am Law 100 earned more than $0.48 million in 2004...It also is worth pointing out that the 26,000 plus equity partners at Am Law 200 firms earn a total of roughly $22 billion (at $0.83 million per partner). This is the same order of magnitude as the total pay to non-financial top executives, investment banking MDs, hedge fund investors, and PE and VC investors.
It is no surprise to hear that partner pay is going up in real terms:
...lawyers have experienced a large real increase in pay over the last 10 and 20 years. In 1984, the average profit per partner at the top 50 firms was $0.309 million or $0.498 million in $2004. By 1994, the average profit per partner had increased to $0.531 million or $0.636 in $2004. And by 2004, the average profit per partner at the top 50 firms had increased to $1.260 million.