What is the typical academic career path following a PhD in computer science? I have a MSc in Physics (computational physics); however, after finishing school I didn't move out of province so now I'm doing software development as a full time job. I miss the challenge of the harder tasks, which do not feel like assembling lego like the ones I currently work on. 

I'm currently debating doing a PhD in Computer Science. Perhaps Numerical Analysis, High Performance Computing. I've also loosely been interested in Artificial Intelligence, but have nowhere near the experience as I would in the other two types. 

In Physics I know you do your PhD followed by a bunch of 2 year post-docs then go into a professorship somewhere; but, I do not know how it works in the Computer Science field. I have a publication in the high performance world from a course I took during my masters, but that is the extent of my experience.

I'm also interested in moving to a more challenging area, but not sure where to be looking. Sifting through the mounds of job posts rarely yields anything that would be in the area I'm considering.

Any advice, thoughts, would be much appreciated.
From my experience, in the UK it tends to be one or two post doc positions and then on to a lectureship position. Comp Sci post docs here are usually between one and three years. 

I get where you're coming from. After my Comp Sci PhD I went into an industry software developer role and 90% of the work just felt mundane. I'm now working for a startup company, which is much more challenging and interesting since the focus is on innovation and creation. That might be worth looking into as it's becoming quite common to find startups sprouting from universities seeking to turn their research into products.