Having coded in many languages, and recently when using MooTools instead of jQuery, i’ve come to realise that most actual programming is pretty language agnostic. What I mean is that most languages do the same thing, just very differently, but it is how you contruct your code that makes you a good programmer
Chances are, if you are good at jQuery you will be pretty good at MooTools (after learning the new declarations etc). The same goes for in a larger extent SQL/MySQL/Oracle or ASP/PHP/Ruby etc.