I know that the architecture is different in symfony 2.0 but im learning 1.4 right now.
I wonder if this knowledge i gain about 1.4 will be usable for 2.0 in some extent or will it be a total waste of time?
I highly doubt they will change everything in the 2.0 version. However, some concepts might widely vary, appear or disappear.
There is no simple answer to that question: If you have plenty of time to learn the 1.4 and nothing else to do, just go. It might be useful in the future to:
Imho, learning something is always a good thing. (Yeah, even learning COBOL !) Wether the "thing" itself is "good" is another question though ;)
I was reading through posts about Symfony 2.0 and I think that @ereOn's idea about learning 1.4 to see the changes in 2.0 is a very good one: you can learn a lot.
I don't have time to, but I will probably try at some point before 2011, just to be able to make a comparison when 2.0 gets out.
This being said, i think Symfony 2.0 is shaping up to be a great project, that will change the way we think about PHP.