Well - took mine in and had an Apple Genius look at it. They ran some sort of hardware diagnostic that you can't get to as a consumer (a large image representing a trackpad appeared on the screen and he ran his finger all around on it - turning the screen from Grey to Green. It checked out OK.
I basically got the "see if you can document the problem better and bring it back" solution. They did request I turn off SmoothCursor - which I use to adjust the acceleration profile between using as a laptop and when I'm in my Henge dock on a 32" monitor. But the settings are stock when I'm not docked, so I'm doubtful.
Doing some of my own troubleshooting. It looks like the palm rejection works fine. If my palm brushes the trackpad while typing the cursor doesn't move (and in fact the cursor bar disappears. What it looks like might be happening is that the the finger tip rejection is not working while you are actively typing. If I just type random letters with my left hand and then touch the trackpad with my right thumb, the cursor bar will move but the typing cursor location will stay put. So not only is this a rejection issue but it looks like the "double tap" to relocate cursor is being activated when the erroneous movement happens.
My suggestion is that everyone call/chat with support and reference this thread. When I mentioned the thread to the chat agent, I got the canned "We have over 300 million devices out there and people often post to the community forums before they contact us" response.
The Apple Genius said the next steps would be to restore my laptop to stock (which I did by the way because the day I got it the FileVault boot sequence fell over and I had to do an internet restore) and then if it still did it (and I could show them it was doing it) they would replace the trackpad.
If I hadn't needed more disk storage and memory for certain applications, I would have been perfectly happy with my perfectly working previous MBP...