The replicator 5.5 firmware included acceleration. I've been fiddling around with it, had every sort of problem this could have and consequently learned a lot.
First of all, "acceleration" doesn't just mean "going faster". It also means "the change in speed over time" and both definitions are true for acceleration in 3D printing. The main feature is that instead of the motor trying to jump to it's maximum speed it accelerates into it. But the result of this is that it can achieve much higher top speeds. The effect of acceleration is subtle, it happens too quickly for the eye to see, but the result on the final prints as well as the printing process overall can be seen easily.
Acceleration is handled by the firmware so even if you don't rebuild your gcode files your prints will benefit from the advantages acceleration. For me this meant an elimination of the "corner ringing", which is those strange vertical ridges I was complaining about before. However the gcode does define the maximum speed which a command can be executed so you'll need to rebuild your gcode files if you want them to go faster.
You can access the acceleration setting on your firmware by connecting ReplicatorG to your Replicator through the USB and choosing "Machine->On Board Preferences" and you'll get to a menu like this:
Jetty's Accelerated Firmware (the general information of which is applicable). Rob had me slow down the A and B acceleration rates and the maximum jerk so that it doesn't strip the filament coming in. I had noticed little flakes of filament all over after acceleration, after adjusting those values it stopped. Reading the notes on Jetty's Firmware I learned about corner ringing and what caused it so I slowed down the X and Y acceleration rates.
Now I'm getting prints as good quality at 60mm/s that I was before acceleration. At 80mm/s I start to lose detail at the corners. However, I'm certainly not done fiddling yet and I'll update this blog if I manage to get excellent prints at ridiculous speeds.