The default web mapping client looks great (AJAX, caching). You can work with multiple services at once. WMS, ArcIMS, ArcGIS Server can all be integrated (projection the fly and transparency) as well as ArcWeb Services. Publishing maps with ArcGIS Server is really easy to do. From inside ArcCatalog all you have to do is right click and select publish. Then you can open them up in ArcGIS Explorer. So if you’ve invested all that time creating your ArcMap documents, you can easily share them with users around the world with ArcGIS Explorer (well and ArcGIS Server).

(side note, someone should sell this service for users who don’t have access to an ArcGIS Server)

Of course you can still create custom applications with ArcGIS Server (and you no longer need ArcCatalog to administer AGS). The ArcGIS Server Manager looks so much more polished than what I’ve seen before (I guess we are getting close to the final release). The real power of AGS is the cartographic capabilities. The maps that get generated are just visually impressive. The online editing tools great. Using AJAX you can digitize right on the web client and they get added to your Geodatabase. (you can even snap to existing data layers). Oh and all this can be done with zero programming on the server side.

Replicating SDE between two different locations is really easy (Think Oracle and SQL Express). This can even be done over web services and ArcGIS Server. As easy as clicking on a Synchronize button, you then send the data back and forth. Our company has tons of small offices and sharing SDE Geodatabases has been quite a bit of work for us, now it is very easy.

Just as easy as ArcMap documents, you can publish models to the Internet right out of ArcCatalog. So from inside ArcGIS Explorer you can connect to these model services and use them. So agencies can share these models and allow others to use them (they didn’t mention but I assume you can use these in ArcMap/ArcCatalog also). Sharing models has never really taken off so maybe this will be the kick that gets it started.