unladen swallow: python and llvm

[Luis M. González]

I am very excited by this project (as well as by pypy) and I read all
their plan, which looks quite practical and impressive.
But I must confess that I can't understand why LLVM is so great for
python and why it will make a difference.

AFAIK, LLVM is alot of things at the same time (a compiler
infrastructure, a compilation strategy, a virtual instruction set,
etc).
I am also confussed at their use of the term "jit" (is LLVM a jit? Can
it be used to build a jit?).
Is it something like the .NET or JAVA jit? Or it can be used to
implement a custom jit (ala psyco, for example)?

Also, as some pypy folk said, it seems they intend to do "upfront
compilation". How?
Is it something along the lines of the V8 javascript engine (no
interpreter, no intermediate representation)?
Or it will be another interpreter implementation? If so, how will it
be any better...?

Well, these are a lot of questions and they only show my confussion...
I would highly appreciate if someone knowledgeable sheds some light on
this for me...

Thanks in advance!
Luis