In 2008, Simon Thum rewrote the X server pointer acceleration code into a complex mechanism that supported better tweaks for a variety of devices. However, a side-effect of this was that synaptics touchpads got accelerated twice, making pointer movement very fast and IMO quite imprecise.
A few months ago, Simon wrote a synaptics patch to pop a synaptics-specific acceleration mechanism into the driver to improve this situation. It's been delayed by me because although I loved it from the first minute onwards, I wanted to get an evaluation done to compare the before and after pointer behaviour in on some objective way (I did get as far as writing nearly all of the code required). Today I gave in and pushed the patch. This study isn't going to happen and I don't feel like holding back something that I believe is a real improvement to how touchpads feel in X.
Now, if you update to synaptics git the first thing you'll notice is that the pointer feels slower. After a few hours or a day you'll likely be used to it, so give yourself the time to get used to it. The new pointer accel code will be in the 1.3 release, which is due out soon (latest for X server 1.9). I'll try to find the time to add some knobs to the GNOME configuration tool by then too.