Well ESRI just released some news about ArcGIS 9.3.1.
What's Coming in ArcGIS 9.3.1?
Here is an item that caught my eye.
High-Performance Dynamic Map Publishing
New faster rendering engine
Outperforms equivalent ArcIMS services.
Produces significantly better-looking maps.
Shortens map caching time.
Quicker, smoother zoom and pan.
If this is true then ArcIMS is truly dead.
There are no more excuses left to not move to server.