I guess I have to learn a new programming language again. This time, it's C#. The reason I have to learn a new language is that we are starting a new software house company. Our first order uses C# as the programming language and .NET as the framework.
Last night I spent a couple hours reading Eric Gunnerson's "A Programmer's Introduction to C#." It's a perfect book for me. It treats the readers as programmers. That is, it skips the introduction on computers and stuff. I knew that already. I taught C++ before (until last semester - this semester I have to many things to do so that I have to delegate this to somebody else) and used Java a few years ago (10 years ago?). The transition from C++ & Java to C# shouldn't be a drastic one. So, I can say that I know C# now. :) I just have to get a compiler to test some of the ideas and get my hands dirty.
I told (and will tell) my students that they have to master more than one programming language. It's just a fact of life. As for me, I lost count the number of programming languages I have learned (and forgotten).