I tried playing with acceleration settings quite a bit, thinking they were the problem - the observed effect was as if mickeys were being inconsistently timed or combined into single events whereby the acceleration layer wrongly interpreted them as rapid motion subject to acceleration. I had mixed results getting semi-usable behavior, but this turned out to be the wrong direction to approach the problem from.
Two properties ended up being key to making the touchpad usable: Synaptics Noise Cancellation and and Synaptics Finger.
With the deault noise cancellation level of 13, holding a finger still on the touchpad resulted in minor "pointer brownian motion"; turning the level down to 0 (as an experiment) made this effect extreme. Increasing it to 20, on the other hand, basically eliminated the effect. It also eliminated the random acceleration and deceleration during movement, which seems to have resulted from the noise component getting combined with actual motion such that the resulting velocity was sufficiently greater or less than that of the actual motion that it affected acceleration.
The other option, "finger", was set by default to 1 for both the low and high threshold values. This worked fine on other touchpads I've used (perhaps it's ignored by them), but it seems to have caused even the slightest touch to be interpreted as a touch/motion, and caused things like releasing after precise positioning, tapping, and pressing the integrated buttons all to result in pointer movement (sometimes extreme jumps). Using thresholds of 40 and 50, which I'd found searching the web for solutions, resulted in a completely non-responsive touchpad. Values of 10 and 20 seem to be working well, and further improved the original jumpiness problem too.
The current (relevant) options I'm using:
Section "InputClass"
Identifier "touchpad tweaked catchall"
MatchIsTouched "on"
Option "HorizHysteresis" "20"
Option "VertHysteresis" "20"
Option "FingerLow" "10"
Option "FingerHigh" "20"
EndSection
I'm posting this in the hopes that it helps others who are having touchpad jumpiness problems with this model or other laptops; other information I found in the process of searching for a solution seemed unhelpful and didn't explain what worked or how it affected symptoms.
Note that the options above are in xorg.conf form, whereas the "properties" earlier in this answer have somewhat different names. This seems to be some sort of xorg insanity that I don't really want to know about. Basically the property names are used if you use the xinput utility to tweak the options at runtime, and the xorg.conf option names are used if you're putting the settings in your xorg.conf or xorg.conf.d directory.
