Well, I decided to give it another try. This time I did a fresh upgrade with the latest EnergyROM, and the first thing I installed after that was WeatherPanel2010... it didn't give me any errors, and the WP Configure Hourly Fix icon is on the start menu... but after a reboot there's no sign of WeatherPanel itself -- the normal Weather tab is there, but there's no extra tab that I can see, either on the current tab bar or on the full list when I bring up the tab settings.
I used the CAB from the first post in this link:
http://forum.ppcgeeks.com/showthread.php?t=7357
Any idea what I'm doing wrong?