I am fortunate enough to now have an educational license of ArcGIS 10, as I am taking a formal class on concepts and methods in GIS.
Overall, I like what I see. But I am a little confused as to why ESRI removed the drop down menus for the Spatial Analyst and 3D analyst. Is there a new reclassify raster tool? A different way to generate a hillshade? Or generate contours over an entire raster extent? I found the old tools by customizing the toolbar, but their icons are an unsightly hammer that makes you think there's something better to be using... (and considering the revamp of Arc's raster infrastructure, there must be).
Update: See this help document on why Spatial Analyst toolbar changed. Hint: Integration. Use the Toolbox and remember to set your Geoprocessing Environment!
Also, the editor has been completely revamped and it took me a few minutes to understand what was going on.
Output quality for JPEG (used in my class) has been improved considerably. So too has loading speeds, in general. Very nice.
One thing I do not like: ArcGlobe is very difficult to navigate around... especially compared to Google Earth. But it is a great idea to make import of elevation data and draping imagery super easy.