Bikes are a wonderfully versatile tool for demos, faster than cops and their dogs and legally equipped with chains so are an instant block anywhere you go, or an instant climbing frame I've heard people proposing bike actions before they never came to fruition but has there already been successful actions using bikes already publicised? I mean more black (bike) blok than Critical Mass or naked bike days? If you think of the police penning people in to underpasses as heavier infantry then protestors on bikes are outflanking light calvalry.