Up on Partnersource is the comparison guide comparing in summary the new features highlighted in each version of GP from V 9.0 onwards.
Check it out here - https://mbs.microsoft.com/partnersource/marketing/campaigns/existingcustomer/msdygp_compareguide.htm?p=5
The document details out the bullet points, module by module and is a great help when you need to point out to somebody what they will gain from an upgrade.
For lots of great posts about GP 2010 new features - http://www.jivtesh.com/2010/04/gp-2010-new-features-system.html,
and here http://www.gpwindow.com/GP_VERSIONS/GP_2010/
You can find posts about GP 10 here - http://www.gpwindow.com/GP_VERSIONS/GP_10/
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