[gentoo-user] clang <<==>> gcc ?

Hi,

before I do a lot of reconfiguring, recompiling and finally
do the same thing again in the opposite direction:

What are the experiences to replace gcc with clang for either
only userland tools or the whole system (with haveing gcc as
fallback)?
Is it worth the effort?
What are the benefits and the drawbacks?

Thanks for any input in advance!
Cheers
Meino