not completely outrageous, although most of the people I know that are billing >= $150/hr aren't billing 2000 hours/year. Actually, even most of the hourly consultants I know that work for themselves aren't billable that often - usually 1000-1200 billable hours between most of the independent IT/tech people I know. Still, even at $75/hour, you're still 2-3x what a lot of people are making, and it's generally only up from there for most people.
Exactly. But that's one of the best parts of software development in my opinion - you can make 3x the median income while living wherever you like and working 20 hours a week (i.e. having time for side projects, or kids)
Note to everyone thinking of consulting and doing this math:
The challenge is that when you bill $150/hr you are not billing 40 hour weeks.
By the way, this is exactly why you need to bill $150/hr (or better, a weekly or monthly rate). If you do 40 hour week math, you think you can bill < $100/hr. And then you are very hungry.
http://en.wikipedia.org/wiki/Median_household_income
In the US, that says median income is ~$31k. You'd be 10x'ing that with a $150/hr consulting rate, which is by no means outrageous.