I've just got access to ArcGIS 10 through my university, and it seems to be far nicer than ArcGIS 9.3. I'm trying to find out what exactly has changed, but the ESRI pages on 'What's new in ArcGIS' seem very vague and marketing-oriented.
So, what have you noticed that's different in ArcGIS 10 (preferably useful too)? If possible I'd like to particularly focus on things that maybe aren't obvious, but are very useful and really improve your GIS workflow.