Yeah, I did the same with my web app scalability contracting work...started at $95/hr, and kept that rate for years, but then when I started getting sick of the business, I started cranking it up. By the end I was charging $150/hr for local work and $3k/day minimum for "have to fly to get there" jobs, and hadn't lost any customers--I was still saying, "No, I can't get out to see you until the week after next, but I'll fix the particular problem you've mentioned remotely tonight when I get back into the office."
Why did you stop at $150/hr if it didn't drop any customers?
I did some basic Windows consulting a few years ago; you know, spyware removal, installing hard drives, etc. My initial rate was $50 / hour, and I was charging $90 by the end of the summer. No one so much as batted an eye at whatever number I gave them. Not a single person tried to negotiate.