Johnson got a lot of interest because he used a bunch start with very little space between his foot pads
Milt Campbell also used the old Bunch Start to good effect, tying Jack Davis's WR of 13.4 at Compton in 1956. It was a real treat to see Milt in Eugene, where he and all other living OlyDecaChamps were honored, even circling the Hayward Field track, even if he did avail himself of a Golf Cart for the circuit, followed by the Thorpe family.
Having copied Milt's start from NJ HS meets, I can attest to its being plenty efficient at getting out of the blocks, per se. Armin Hary's exaggerated long push into an elongated (and powerful) first stride had an early effect on rethinking the entire Start/Acceleration phase into more of a piece, if you will.
I'd be interested in hearing some bio-mechanical analysis--which we may get from Ato Boldon in the inevitable long buildup to the 100 m--of Usain Bolt's own version, which seems to me rather disjointed, verging on that 'jumping out' mentioned above.
One sidelight on 'pickup': too many Sprinters seem to settle for keeping their heads down w/o effectively keeping low and driving. [In the same vein: Dwight Stones's insight into that woman HJ'er at a recent DL event (Monaco?) whom he accused of fooling herself into thinking she was correctly leaning into her "curve" when all she was doing was bending a bit at the hips.]