After a shaky start with their pre-conference workshops, the actual conference was fantastic.
All four of the Keynotes were fantastic - and quite motivating.
Unlike other conferences I've attended where the entire content is based on future, unusable at work, new products. Or, they all seem to be doing nothing but promoting their book. Well, MIX09 was, of course, a little of both of those, but it was also so much more.
There was a lot of "soft" information for the designer on the UX or User Experience. Since I am mostly a backend developer, I gained a lot of insite on the design side. There was also quite a bit of information on silverlight - including animation.
So, all in all, for me MIX09 was an unqualified success.