I just upgraded the forum farm to SP2.

After SP2, run the “STSADM –o preupgradecheck – localonly” to check that your farm is capable of an upgrade.

A great tool of assist in finding what the “missing” features are:

http://code.msdn.microsoft.com/WssAnalyzeFeatures

To check or remove invalid features on SharePoint 2007 site:

1. 1. Run the WssAnalyzeFeatures tool and view the Problems Log for invalid feature id(guid’s)
2. 
3. 2. STSADM -o deactivatefeature -id %featureIdFromLogFile% -force
4. 3. Run the WssAnalyzeFeatures tool and see if the problems we're resolved.
5. 4. If feature can't be removed or is in a subsite for a failed WSP solution uninstall, try running the WssRemoveFeatureFromSite to forcefully invalid old features.
6. 5. Remove the feature ID's until WssAnalyzeFeatures shows no errors.

Another tool you can use to remove “missing” features is:

http://featureadmin.codeplex.com/

Here’s how it should look like after removing the “missing” features:

Cheers,