I own a consulting firm with now about 15 active (>= 100% billable) consultants. I have been a consultant for about 7 years now, and it's been extremely kind to me. The sky is the limit, but there are a lot of additional demands that many people seem to be unable to meet, or at least unable to meet for an extended period of time:
1) Hours. Consultants are almost always the ones putting in the most hours. I've had entire years where I average 65+ hours a week. Sometimes I've worked 100 hour weeks. You'll work the hours of a doctor without the prestige to go along with it.
2) Complexity. Consultants are most often called to work on the more complex aspects of a project; if they had in-house talent, they'd use them. This often means working in areas where you're pioneering new ideas, and this can mean a lot of very extreme stress. I've worked on software to do everything from getting a Pocket PC to sync with SCO Unix to robotics, and all along the way the efforts were punctuated with moments of extreme stress. It happens.
3) Change. Consultants have to be flexible. You can't expect to have your 8-5 stability with an office that looks the same everyday. You might very well have that, but what will make you successful is a great ability to adapt; you have to anticipate change and embrace it.
That's it for now. Yes, it can be very lucrative. As someone else said, $50-75/hr is on the low end, but it depends on the type of work. Simple web work doesn't command a great rate, but top software architects/leads can easily command ~$100/hr or more. I can tell you that there's not a person on my staff that makes less than 6 figures.
Once you've been in consulting for a while, you'll find that it's not difficult to find new opportunities.