How to deal with faulty features

Before upgrading to SharePoint 2010, you should run preupgradechecker and Test:SpContentDatabase..

Preupgrade checker should be run on the 2007 instance and Test:spcontentdatabase should be run on Sharepoint 2010.

After you run the preupgradechecker, it creates an html file containing your farm details. In my case, there were lots of missing features!
The entries were like these:

Name = [Unknown], Feature id = [5ac519ce-6bf2-842c-485c-04efe522a2dc], Reference count = [1], Scope = [Web], Status = [Missing]

Name = [Unknown], Feature id = [c5e293c8-a4c6-8607-5505-7a2a77a9800e], Reference count = [1], Scope = [Web], Status = [Missing]

Name = [Unknown], Feature id = [68f713c6-1fc8-d110-e819-ce7d59518f60], Reference count = [1], Scope = [Web], Status = [Missing]

Name = [Unknown], Feature id = [564a2b98-aec8-e5f5-7e94-8096d64fe16c], Reference count = [1], Scope = [Web], Status = [Missing]

Name = [Unknown], Feature id = [a28a2e77-9525-4c9c-ad79-e0b6252395e8], Reference count = [1], Scope = [Web], Status = [Missing]

While searching on the internet, I found that tool which is very handy to remove problematic features:
http://featureadmin.codeplex.com/

Of course, test it before you try it ;)
In my case I perform a database attach upgrade so it's easier to test.