Switch from pure mathematics to machine learning as postdocs? I'm a first year postdoc in pure mathematics (geometry/topology with strong background in analysis) with undergraduate statistics and probability background (with also measure theoretic probability). I also have some programming knowledge in ForTran, C and Matlab, but I never used them in my pure mathematics career in my graduate school for the last 5 years.
In my next job, I'm considering doing a postdoc in machine learning (ML). The reason behind this switch is: I'm satisfied with my pure knowledge so far and have been wanting to see some real-life applications of mathematics, and also keep my options open in both industry and academia.
My questions are:

How hard is this switch going to be? I guess I've all the required mathematics background, but will it be hard to pick up the necessary computer science skills, even if I work in more theory-oriented problems?
What exactly are the programming knowledge I need to master to work in ML?

Is there a website/email-list where I can get notifications on jobs in machine learning? I'm looking for jobs in Europe mostly, but information on the US would also be welcome.
1) How hard is this switch going to be? I guess I've all the required
  mathematics background, but will it be hard to pick up the necessary
  computer science skills, even if I work in more theory-oriented
  problems?


Not a problem: picking up the math associated with ML. You've got the right background and you'll find it easy to understand the papers after an initial learning phase.

Potentially a problem: understanding why certain questions get asked and what's considered interesting. This is where mathematicians and computer scientists tend to diverge, and translating your intuition for questions might take some time. But a more mathematical mindset can also lead you to ask interesting questions that CS folks are NOT asking !


  What exactly are the programming knowledge I need to master to work in
  ML?


Depending on how theoretical the postdoc is, anywhere from none to R, python and matlab, and maybe even some distributed large-scale learning framework like GraphLab. But you should definitely get some familarity with the first three - ML is a good example of "no problem formulation surviving first contact with the data". 


  2) Is there a website/email-list where I can get notifications on jobs
  in machine learning? I'm looking for jobs in Europe mostly, but
  information on the US would also be welcome.


One good mailing list is ml-worldwide. Another is the Google group ml-news.