My understanding of it is that you're given a user defined amount of time in which to play in real-time (say 16 beats or 4 bars of 4/4 time) before that 'buffer' is then sent to all other players and likewise with them. So you're never really playing at the same time as them, just playing over the 4 bars before them and they play (in real-time) )over your previous 4 bars.
Actually Giuseppe, I play keyboards, utilising the amazing sampler that is Linuxsampler for acoustic instruments and a combination of the Bristol Mini-Moog emulation and Rakarrack FX for nice distorted lead sounds. My nick on ninjam is Andrew.
Andrew! Sounds interesting and actually one musician already invited me, but it did not work out due to connection problems. Can you explain how exactly jamming works?