Around 2010, Flash on anything other than Windows was notoriously craptastic -- to the point that Apple refused to support Flash in their mobile browser.
Nowadays, that same 2010 Mini could probably stream Netflix reliably, since it'll be decoding HTML5+DRM instead of Flash.
Yup, I have a 2009 core 2 duo mac mini and it does netflix just fine thanks to html5 video. It still does everything I need reliably (web browsing, non-vm web dev, ms office), but I will upgrade to the new mini and hand this one off to the kids.
Nowadays, that same 2010 Mini could probably stream Netflix reliably, since it'll be decoding HTML5+DRM instead of Flash.