Inspired by the diagonal rods on my Rostock and borne by the desire to do no filament retraction, I designed this ultralight carbon fiber Y-carriage. Don't know if it'll fit on a stock Prusa, mine's pretty heavily modded.
Picture of print (from: thingiverse.com/thing:19900) shows results with XY jerk at 40 and 400 mm/s travel speed, 60mm/s print speed and ZERO retraction. Almost where I want it.
The cogs n' dogs stuff is needed (http://www.thingiverse.com/thing:26682) and I use my belt terminators which will be posted someday soon.
Given my limited understanding of the motion control in firmware, I believe the thing to alter is jerk and max acceleration, which I'll be toying with. More ideas are certainly welcome.