I'd just like to mention that I needed to test something on my 1.5.4 installation with Timing and Estimation Plugin (which I am using on our Trac 1.4.2 installation). So, I updated the plugin to run on Python 3 with Trac 1.5.4.
I'm not exactly a power-user of this plugin, but we do use it for the more basic functions.
Interestingly, when moving to the new Trac, the plugin needed to update the database. Seems like there was a ticket type that was blank or something like that in the old database, and it wanted to update to squeeze it out, as far as I can tell. I'm not sure why that would be the case. Most other plugins don't seem to have a problem using the pre-existing database tables.
I left a patch at Trac-Hacks in ticket 13732