I am using Eclipse 3.4 (ganymede official, not the service pack).
I have an update site that organizes features into categories; everything looks great in the editor and in the XML.
Once the site is online, accessing it in the usual manner tells me that all the features are "uncategorized". I've tried from multiple computers running 3.4 and the same problem persists.
What is curious is that I used Eclipse 3.3, and it saw the categories well, though of course it wasn't able to instlal the plugins which are made from 3.4.
Am I doing something wrong or is this a known problem?
It appears to be a known problem, due to the new 'p2' provisioning system.
See this discussion, and this bug. What it seems to say is... "stay put until 3.5M3, and then try it again".