I have Amplitube. The Groove3 tutorial on it (listed in this specials list for just $5) was really helpful to get oriented. GR5, TH2 and others don't have a lot of examples or reference materials. Having a several hour microscopic walk through of Amplitube gave me some great tips and I use what I learned.
So for $5, that's a no brainer, even if you haven't started using Amplitube yet this would be a great way to investigate it.