The clock just seems to freeze at random. I'll update the ticket if I notice a pattern, I just figured out that this is happening today. The clock displayed 2:04pm for 20+ minutes, until I suspended the computer around 2:30. Then I opened the computer back up around 5pm and the clock is displaying 5:04pm even now (at 5:30).
In the properties dialog, I have it set to:
Format: Time only
Font: FreeSans 9
I just changed the format to "11:59 pm" (instead of custom) and the clock updated. It appears to be unfrozen now...
Running xfce4-datetime-plugin version 0.6.1-3 on Ubuntu 11.10.
Mass-reassign all bugs from florian@ to goodies-dev@, thanks for the maintenance work! (and sorry for the bugmail spam..)