Had an original idea for a start-up...but
jnovek: "Usually I spend it reading all sorts of ebooks and papers and trying to learn new skills."I suggest you switch gears and spend your free-time coding :-).Pick some technology you think you want (you can change your mind later) and start doing side projects in it.  Do up your personal home page.  Make a google maps mashup.  Some stuff to familiarize yourself with the technology.There have already been lots of good suggestions on which technologies to use.  Try a couple different ones.