Performance with Computers/DJ-ing

[Your Name <switters@earthlink.net>]

I'm curious as to how people are using their computers for live 
performance.
How do you manipulate it?  How much is live vs. sequenced/pre-recorded?  
Are
there any DJ/Turntablists mixing with vinyl and a computer?  I've thought
about trying to incorporate my G3 Powerbook into a live situation but I'm
uncertain as to what a performance would constitute beyond pressing play 
and
twiddling with on-screen faders.  As a DJ, how does one perform a track
you've recorded and released live?  For instance when the Chemical Brothers
perform, what exactly are they doing?  I know Portishead press-up vinyl of
the beats and other materials they've recorded but what is the process of
working with such material. As I said, I'm curious.

Please no slander or flame wars over the validity of such performances, all
such debates are simply displays of subjectivities in conflict.  I would 
like
to hear from people about actual techniques, process and performances.

Best, Sean