I just updated to r551 and noticed am getting the following error:
Smarty error: unable to read resource: "Home/templates/header.tpl"
The call is on line 55 of Home/templates/index.tpl. From looking at changeset 551 it appears header.tpl is a new file that Matt just forgot to add to the repository.
My guess is that header.tpl contains the code for the Piwik - Open Source Web Analytics banner that has been at the top of the application.
I fixed this a while back, sorry for not notifying!