Q: Tracker pad erratic since 10.9.3 update

There are several possible causes for this issue. Please take each of the following steps that you haven't already tried until it's resolved. Some may not apply in your case.

1. Follow the instructions in this support article, and also this one, if applicable. A damaged or defective AC adapter could be the cause, even if it's the right kind.

2. Open the Bluetooth preference pane in System Preferences and delete all pointing devices other than the trackpad, if applicable. Disconnect any USB pointing devices. By a "pointing device," I mean a peripheral that moves the cursor, such as a trackpad, mouse, trackball, or graphics tablet. A plain keyboard is not a pointing device.

3. Start up in safe mode and test, preferably without launching any third-party applications. If you don't have the problem in safe mode, but it comes back when you restart as usual, stop here and post your results. Do the same if you can't start in safe mode. If there was no difference in safe mode, go on to the next step.

4. Reset the System Management Controller.

5. If you're using a Bluetooth trackpad, investigate potential sources of interference, including USB 3 devices.

6. A swollen battery in a portable computer can impinge on the trackpad from below and cause erratic behavior. If you have trouble clicking the trackpad, this is likely the reason. The battery must be replaced without delay.

7. Press down all four corners of the trackpad at once and release. If there's any effect, it's likely to be temporary, and the unit needs to be serviced or replaced.

8. There's a report that a (possibly defective) Thunderbolt Ethernet adapter can cause the built-in trackpad of a MacBook to  behave erratically. If you're using such an adapter, disconnect it and test.

9. There's also a report of erratic cursor movements caused by an external display that was connected but not turned on.

10. If none of the above applies, or if you have another reason to think that your computer is being remotely controlled, remove it from the network by turning off Wi-Fi (or your Wi-Fi access point), disconnecting from a Bluetooth network link, and unplugging the Ethernet cable or USB modem, whichever is applicable. If the cursor movements stop at once, you should suspect an intrusion.

11. Make a "Genius" appointment at an Apple Store to have the machine and/or external trackpad tested.

I noticed the same thing.  My trackpad is acting up all of a sudden and decided to google it.  This is the first link I found and it was posted earlier today...  Coincidence?  Probably not. 

I have experienced exactly the same problem. None of the conditions in the support response apply, and I'm running a current model i7 13" Macbook Air, in good condition and functioning brilliantly up until this update.

As someone who also runs Linux boxes and Android devices, where Apple keeps telling us that developers are handicapped by having to develop for unknown hardware configurations, I find it ironic that they can't handle trackpad drivers for their own kit. The Debian builds on the machine seem to work pretty well.

I have found  complete reboot seems to fix the issue for the next few hours. But changing the trackpad preferences, backwards and forwards, doesn't. Sometimes the pad recognises only fone ingure, sometimes it behaves perfectly.